The Second Best Place To Set a Bomb

An airplane I flew today had an oddly located fire extinguisher. While looking up the rules in CARS 525 on where the fire extinguisher has to be with respect to the pilot's duty station, I found some rules on airplane interior design that weren't there when I learned to fly.

(c) An aeroplane with a maximum certificated passenger seating capacity of more than 60 persons or a maximum certificated take-off gross weight of over 100,000 pounds (45,359 Kilograms) must comply with the following:
(amended 2010/06/16; no previous version)

    (1) Least risk bomb location. An aeroplane must be designed with a designated location where a bomb or other explosive device could be placed to best protect flight-critical structures and systems from damage in the case of detonation.

According to this FAA document the Least Risk Bomb Location (LRBL) has been a thing since approximately 1972. The crew should be aware of the LRBL, but we can be forgiven for not knowing, as the guidance document includes a prohibition on marking it with cute international graphics or bilingual block lettering saying something like "place unattended bombs here." For more information on determining the best location of an LRBL, you may consult a document entitled “DHS Recommended Least Risk Bomb Location Procedures for Airlines,” Sensitive Security Information (Limited Distribution). The FAA will need your letterhead and an e-mail address. I hope they do more than glance at the letterhead and go, "ooh, it's embossed, and someone used expensive design software on this, they must be a legit airline. Quick, e-mail them the secret LRBLs." Probably they have more secure procedures than that, but the whole letterhead thing is so quaint that I had to make fun of it.

If you don't have a need to know, or a fancy letterhead, you can still find out about LRBLs. The public document is interesting enough, with little diagrams and recommendations on how the LRBL should work. If you click through to look a the document, don't forget to scroll down to the name of the person responsible for it, and imagine how much fun he has at airports when he's "randomly" selected for special screening based on his name, and then they discover his carry one is full of Sensitive Security Information about where to put bombs on airplanes. Whatever city he lives in, that's where the meetings are.

The airplane I fly does not have a passenger seating capacity of more than 60 persons. Were we to discover a bomb on board, I would direct it to be thrown out the emergency exit. Such a measure would be an extreme emergency procedure for me, but its physically impossible to open an exit on a pressurized aircraft in flight, because the exits are plugs held in place by the pressure. The only way to open one would be to blow it up. The implication of the document is that that's kind of what some LRBLs do. It also points out that decompression is less harmful if it's not done explosively, so I imagine the "oh no there's a bomb on board" procedure involves an emergency descent and controlled depressurization. The descent would be so that by the time the airplane was depressurized and the oxygen in the generators was exhausted, the ambient oxygen would be sufficient to sustain the surviving passengers.

    (2) Survivability of systems:
        (i) Except where impracticable, redundant aeroplane systems necessary for continued safe flight and landing must be physically separated, at a minimum, by an amount equal to a sphere of diameter
        D = 2 v (H0 / P )
        (where H0 is defined under 525.365(e)(2) and D need not exceed 5.05 feet (1.54 metres)). The sphere is applied everywhere within the fuselage limited by the forward bulkhead and the aft bulkhead of the passenger cabin and cargo compartment beyond which, only one-half the sphere is applied.
        (ii) Where compliance with subparagraph (c)(2)(i) of this section is impracticable, other design precautions must be taken to maximize the survivability of those systems.

I think that is meant to imply that if you want to take out redundant systems, you'll need more than one bomb. Plus I'll throw you overboard with your bomb.

    (3) Interior design to facilitate searches. Design features must be incorporated that will deter concealment or promote discovery of weapons, explosives or other objects from a simple inspection in the following areas of the aeroplane cabin:
        (i) Areas above the overhead bins must be designed to prevent objects from being hidden from view in a simple search from the aisle. Designs that prevent concealment of objects with volumes 20 cubic inches and greater satisfy this requirement.
        (ii) Toilets must be designed to prevent the passage of solid objects greater than 2.0 inches in diameter.
        (iii) Life preservers or their storage locations must be designed so that tampering is evident.

What and ruin the plot of so many bad airplane movies? At least there's no rule about disabling the secret passage out of every airplane washroom into the giant avionics bay. I think the life jacket one is interesting. I've never noticed the lifejacket pouches to appear particularly tamper-resistant.

(d) Each chemical oxygen generator or its installation must be designed to be secure from deliberate manipulation by one of the following means:
(effective 2015/03/20)

    (1) by providing effective resistance to tampering,
    (2) by providing an effective combination of resistance to tampering and active tamper-evident features,
    (3) by installation in a location or manner whereby any attempt to access the generator would be immediately obvious, or
    (4) by a combination of approaches specified in (d)(1), (d)(2) and(d)(3) of this section that the Minister finds provides a secure installation.

(e) Exceptions. Aeroplanes used solely to transport cargo only need to meet the requirements of (b)(1), (b)(3) and (c)(2) of this section.
(effective 2015/03/20)

I haven't yet seen a bad airplane movie in which the bad guys repurpose the oxygen generators as poison gas grenades, but maybe it was so awesome I forgot.

More Pressure

These puppies have pressurized airframes, and so have an entire system to control the coming in and the going out of the air. Like the other posts in this series, this one will concentrate on what I have to know, with little concession to those who don't know what I'm talking about, but I find it most useful to explain things in quirky ways, so it may be interesting anyway. And feel free to ask questions. You may hit on something I ought to know. The pressurization system includes static ports (holes in the airplane used to sense how rarefied the outside air is), bleed air (compressed air from the engines), an outflow valve (a hole to let the air out), a dump valve (a bigger hole to let all the air out if you need to) a controller (a gauge in the instrument panel with a dial and a knob that you use to tell the airplane how much air to keep inside and how much to dump overboard), a couple of safety valves, a bunch of lines and relays and things, and a couple of gauges that tell you how all that is going for you.

The maximum differential pressure between the inside of the airplane and the outside of the airplane is 7.0 p.s.i., giving a sea level cabin at 16,800' and a 4600' cabin at the service ceiling of 25,000'. The various gauges work kind of like an altimeter or a VSI, comparing reference pressure, cabin pressure and static pressure as appropriate to drive indicator needles. Pneumatic relays associated with the controller create pressure differentials that can drive valves. There is more detail available on this system, but all they need me to know is that I turn knobs to set the controller and that the controller commands things to happen according to my whims, such as allowing or not allowing air out the outflow valve in order to hold the cabin pressure at the set value. The outflow controller will also open if the differential between cabin and external pressure exceeds 7.25 p.s.i. or if the outside air pressure exceeds the inside. When these things aren't happening, a spring holds the outflow valve closed. The training manual describes a number of interesting diaphragms and valves that activate the opening and closing of the outflow valve under different conditions, but they want me to say only that it is opened by vacuum and closed by a spring.

The cabin air pressure dump valve has a similar pressure release function, as the outflow valve, both in the overpressure and underpressure case, plus it can be opened with an electric solenoid valve to dump the cabin pressure, equalizing the cabin with the outside atmosphere. Technically the electric solenoid connects the dump valve to vacuum pressure, causing "the dump valve diaphragm to open the dump valve." But I think I would lose points for getting into that detail, and should say that it is opened electrically, using a solenoid that gets its power from the left essential DC bus, transferable to the right. When pressure is dumped, it is dumped into the nose baggage compartment, which happens to be the same place the alternate static source gets its pressure, so a cabin dump should not be performed while instruments are operating on the alternate static source.

There is also a manual control valve that can be used to bypass the pressure controller and directly adjust the opening of the outflow valve. For the manual valve to have an effect, a switch on the console must be moved from auto to manual. This is the sort of thing I expect from pressurization systems, so you can perhaps get an inkling of the sort of things pilots were yelling at the screen during Snakes on a Plane, which if I recall correctly was the movie in which they solved an overpressurization problem with gunfire through the fuselage.

More interesting than the magic boxes and networks of vacuum hoses is how I use it. First some terminology. The cabin altitude is the altitude I'd be at in an unpressurized airplane for the cabin to be at the pressure it's at. The rate of climb or descent of the cabin is the rate of change of the pressure there. With pressurization, the cabin altitude can be different than the airplane altitude, so that we don't have wear oxygen masks above 13,000'. To set the pressure I dial the controller so that the bottom part displays about a thousand feet higher than the altitude I will be flying at. That way the arrow points to the minimum cabin altitude I can maintain for the flight, without worrying about it banging up and down on small altitude deviations. If the world were flat, I could mostly leave it at that, but airports are at all different elevations and this introduces some issues.

To begin with, the airplane is not pressurized on the ground. It's bad for the airframe to land pressurized, there's no point, you'd have to depressurize to open the door, and why pump up the cabin to an altitude lower than the one the passengers walked in the door at? It wouldn't work anyway, as the dump valve is linked to the squat switch and if it's working properly it stays open on the ground. If you set the cabin altitude to sea level then took off from an airport with a 3000' altitude, as soon as the weight came off the wheels, the dump valve would close and the airplane would try to pressurize the cabin down to sea level. That's just weird, and most people don't like the feeling on their ears when they are descending. The whole point of a pressurized airplane is to avoid that as much as possible. So I set the cabin altitude to the higher of what I will be maintaining in cruise and the departure airport pressure altitude plus a thousand. So coming off a 3000' airport I'd set it to 4000' if I was cruising at 20,000' or below, but if I was going to cruise at 25,000', I'd set the cabin altitude to 5000' or so, because the controller says I can maintain a cabin altitude of 4600' at 25,000'. So I'd take off, the dump valve would close, and the cabin pressure would be 3000'. The controller would not start pressurizing the cabin because it was already at a lower altitude than selected. It would let some air leak out as we climbed to 4000' and then it would stop letting air out and start hoarding it, to keep the cabin altitude at 4000' as the airplane rockets on up to cruise altitude. At top of descent I would set the controller to maintain a cabin altitude about 500' above the landing airport, and a descent rate of 500 feet per minute. If the landing airport were at 1000', that would take five minutes, and meanwhile I could be plummeting through the real descent at 3000 fpm without hurting anyone's ears.

The thing to watch is if the cabin is going to take longer to reach the landing elevation than the actual airplane, because you can "catch the cabin." The problem with that is that the cabin cannot be at a higher altitude than the airplane, because that would mean less pressure inside than outside, and the pressure vessel is only designed to take pressure from the inside. The outflow valve will automatically let in outside pressure if it exceeds the inside pressure, so as soon as you catch the cabin, you feel the descent just as you would in an unpressurized airplane. So to prevent this you can increase the descent rate of the cabin, decrease the descent rate of the real airplane, or level off at an intermediate altitude to allow the cabin to get ahead.

The pressure comes from P3 bleed air, from the second stage diffuser. I'll probably have much more to say about this system once I've actually worked with it.

When I need a break from hard studying work, I start filling out all the company forms. I have to put my height and weight on my security pass application. I'm 1.5 kg above my target weight. I omit the half and put myself down at one above. Or I could wait a week and lose those last 1500g and put down what I should be. I look way better now. You don't notice the little layer when it creeps up on you. A little more butt toning and I'll look the way I want to.

Safety is What You Make It

When you fly, even if you're a jaded, experienced traveller, and know how to hide your notebook computer under your jacket when the flight attendant looks at you, please put it away. Stow your carry on baggage completely and don't hold heavy objects during takeoff and landing. Fasten your seatbelt tightly. Pay rapt attention to the safety briefing and any instructions from the flight attendants. I understand that a certain joking fatalism is a common defense mechanism to avoid thinking about what could happen, but it's better to think and be prepared. There are survivable airplane crashes. Here's a B737 torn apart by impact forces, but the only death associated is suspected to be a heart attack and not the immediate result of injuries sustained. There was no fire, and clearly the nearest emergency exit to many people would be the gaping hole where the fuselage ended, so no one was trapped.

I don't have any information on what happened to cause that crash. It sounds like they might have encountered a sudden downdraft. I'll try to follow up when the investigation reports a result.

Another story, related only in that it takes place in Colombia has a reader of this blog flying as a passenger in Colombia, in what he thought was a small pressurized airplane, about ten to fifteen passengers on board. And it was raining inside the plane. It's not clear if it was raining outside and leaking or if there was condensation leaking out of the headliners, but the folks in the back were getting wet. A passenger yelled up to the cockpit that it was raining inside and we were all going to die. The FO turned around and his enraged response was, "Callate por favor! Tenemos problemas mas grande aqui al frente ... no podemos ver nada, hay montañas en todas partes aca y hemos perdido contacto con... ."

I'll give the Spanish speakers a chance to gasp and or laugh at that while the others can wonder what they'd think about the FO yelling incoherently at them. He was yelling, "Would you please shut up! We've got bigger problems up front ... we can't see anything, there's mountains everywhere, and we've lost contact with ..."

The person who told me that story says he prayed until a safe landing and never again took a "non-reputable" airline in South America. Ironically, the day before he had read a very similar account in a story from 1945. Some things never change.

It's not that people in Colombia cannot fly safely, maintain airplanes safely or do everything else to any arbitrary safety standard. There is no absolute safety, only a level that you choose to maintain. It's just that the normal level of what is generally considered to be 'sufficiently safe' is different from place to place. The roads in different countries aren't built to the same standards; South American buses are a cliché. A lot of it is money: money for parts, inspection, training, maintenance and infrastructure too. It would cost the same amount of money to build and maintain one road to US department of highway standards as it costs Colombia to build and maintain any number of roads. The degree of safety in any organization is balanced between money available, regulatory pressures, regulator oversight, competition on price, customer demands, and inertia of the current practices and procedures. In any organization you get the safety you work and pay for. There are freak accidents, yes, but there are also freak 'almost accidents' that warn alert companies of the possibility of actual ones.

If I Did It

So, as I said, the instructor quit an hour early so as not to miss his favourite TV show, leaving an unbooked hour in the sim. After discussion with John, I've decided to document as follows. If I had a chance to fly the sim for that hour, this is how it went.

I'm in the left seat, a colleague of John's is in the right, and John is running the sim. Rather than spend precious minutes starting up and taxiing, I ask John to position the aircraft holding short of the runway, engines running. The same eternal twilight prevails. Maybe it's the default. It's commonly used in sims, because you can still see well, but the brain accepts that indistinct visuals are caused by poor lighting conditions, heightening the efficacy of the illusion.

Not Me (nor Lee), doing prestart checks in an Australian C-130

I call for the pre-takeoff checklist, which I had thought was displayed on screens on the glareshield, but now that I can see it close up I find that the centre panels are nav and radio frequencies (funny to see numbers starting with "2" up in the UHF range) and it's where you set the autopilot parameters, which is why they were looking at it at checklist time. You can sort of see them in the photo. My copilot, whom I will call Lee, because it's awkward to keep calling him "the guy in the right seat," says "it's a flow," meaning that it's a silent rechecking of systems. I give a takeoff briefing consisting mainly of the appalling, "I'm going to push everything forward and rotate at ... umm, what's it say on the TOLD?" and "then we'll make it up as we go along." We obtain a takeoff clearance, and then I taxi onto the runway.

You might wonder why I didn't just ask him to start it up ON the runway, like the default in Microsoft Flight simulator. I do want to see what it's like to taxi, not just to know, but because a take off run is transitioning from taxiing to flying and let's give me a chance to see how this thing works before I'm actually taking off. Oh and there's a wrinkle that I very almost forgot. In an airplane this size there is no rudder pedal-nosewheel steering linkage. I have to steer with a separate wheel. It's like the steering wheel on some buses: a normal steering wheel with a knob on it so you can crank it fast. It's weird to have airplane steering in my hand.

With the right hand, it's quite easy to push four power levers forward. They've been designed to act as one, or as two for differential power. Oops, it's too easy. You have to put the power up and wait for things to happen when the airplane is this big. Maybe I'd be more intimidated by this airplane had I had to walk up to it and climb into the cockpit instead of walking across the little bridge into something I could see wasn't much bigger than a minivan. I stay on the simulated runway and get the thrust under control.

Centred -- more or less -- on the runway, that again-forgotten 'go past before you need to turn' thing, and my slowness on the nosewheel crank worked in my favour here. You don't have the same foot feedback on whether the nosewheel is centred like with rudder-linked steering. You have to look at the markings on the pointer by the steering wheel to see if the nosewheel is back in the middle after a turn. I eat up a few hundred feet of runway experimenting with the steering and getting the airplane properly centred with the nosewheel straight, then I stop and look at Lee. "Ready?" Some aircraft have lineup checks or "below the line" items on the runway. If this one does he's snuck them in, because he just says, "Ready, Captain." John must have paid him to say that. I grin like a kid and push the power levers forward.

Oh. Yes. Baby. This is a twenty million dollar sex toy. Size matters, as long as it's got this much thrust. In the back of my mind is the knowledge that lurks there on every real or simulated takeoff that it may be an abort, but I do everything but call out "don't stop!"

It climbs like a bat out of hell, and is remarkably stable doing so. I call "Gear up" and find myself hunting for an HSI or other directional indication to maintain my heading. We're in VMC but even with all these windows, I can't see a ground reference at this climb angle.

"Heading information?" I ask.

John just says, "that's fine right there." He thinks I was asking for a heading. I figure it out. It's on the HUD, like a compass, only forward, which is backwards for a compass. Don't ponder that too hard. I'm right side up and have nowhere to go in particular. I also have to clean up the power. I'm so far behind this plane I wouldn't get hurt in a crash.

"What torque do I set for the climb?" Lee's hand beside me does it. The beauty of having at least one crew member who knows what he's doing. Wait, there are no propeller levers. "Where are the propeller controls?" The throttles are just throttles, but this is not a jet, it's a turboprop. You're not going to tell me it has fixed pitch propellers?! Apparently it's automatic. How cool is that? I have no idea how it works. I could look it up, but then this blog post would be even later.

We're through ten thousand feet in the time it takes me to figure out how to look straight ahead of me and accept that I have no propeller levers. I level off and then make some shallow turns to look around, and get the feel of the airplane. It feels very much like an airplane. Knowing the way a simulator works: tipping and lurching to simulate various kinds of motion, then sneaking smoothly back to the middle so it's ready to do that again, I had intended to try and trick it and come up with a scenario that would allow me to notice the little man behind the curtain, but even as a passenger it didn't occur to me during maneuvers that there was anything going on other than airplane physics. Now that I can try it, I want to think about trying the plane not the sim.

There's a reason the trainees were doing steep turns and stalls. It's not just that they're flight test items, but that's how you tell what an airplane does. You need to know how it responds to roll, pitch and power inputs. On an examination you demonstrate a steep turn to prove you have mastered these controls. On a test flight you find out how the airplane behaves. On a lesson you find out how the student behaves. I find out whether I'm going to make a fool of myself.

I see no traffic. (It doesn't matter that you're in a glorified box on a stick, if you were properly trained you can't do a turn without checking for traffic) and try a forty-five degree turn. Look at the horizon; roll smoothly through thirty degrees; climb two hundred feet as I add way too much thrust. "Easy on the rudders!" advises the right seat pilot. It's surprising he can speak, given how hard he must have been biting his tongue up to now.

I roll out, using much less rudder, readjust the power, and then try again. This time smoothly, easily, lock it on the horizon and carve a semicircle in the sky, and then back the other way to where I started. It's really just like my regular ride. I usually screw up the first one in recurrent training, too, because due to my regular payload I'm operationally forbidden to bank over 16 degrees, often less. I trust that the way the simulator feels is very much the way the actual airplane feels, but it doesn't feel like I'm hauling around three Humvees, 64 paratroopers or almost 30,000 kg of fuel.

"What weight is it set at?" I ask, scanning the areas where the guys seemed to have been looking when they did their fuel calculations. I don't have their benefit of groundschool, study manuals (I asked, but they were all "not to be transmitted outside the department"), or non-motion cockpit trainers. "Can you adjust it so I can feel it at max gross?" John does so, and I do another steep turn. Now I need more power.

"What is the stall speed in this configuration?" There's a TOLD indicator on the centre console. I think it was one thirty something. Forgive me for not taking notes. Those sinusoidal fans Angus mentioned seem to have done their job. Or maybe it's the week or so delay in writing it up. So fly plane, reduce power, fly plane, reduce power, hold altitude, trim, airspeed dropping. "Hey, I want to hold it in slow flight for a moment," increase power, keep nose up, hold altitude, now I get to use the rudder a bit more, but I guess it has a yaw damper, because not as much as I would expect. I'm trying to balance it on the edge of a stall. There's something amazing about the skills I learned in a Cessna 152 being applicable to something that probably needs chocks bigger than an entire C152. I hold the attitude and reduce the power a bit more.

WHACK!

I was intending to stall it, and knew it had a stick pusher, but the movement of the stick actually pushing takes me by surprise. It's like a flight instructor angrily grabbing the controls, or the first time anti-lock brakes makes themselves felt under your feet. The pilot is supposed to push the stick forward to get the nose down if the airplane stalls, but this airplane isn't taking any chances that I'm stupid or slow, so it shoves it forward itself. Many smaller airplanes are aerodynamically built so that the airplane noses down at the point of stall. This feature replicates that. I increase the power as I should for the stall recovery. The familiarity of that maneuver--stick pusher notwithstanding--is a testament to this being a historic airframe, predating airplanes too fancy for humans to fly them without computer stabilization. "Take it down to a minimum weight," I dictate to John, words like 'could you please' completely lost in the combined spirit of scientific investigation and pilot-in-command.

I stall and recover again in level flight, letting the stick pusher push one hand while the other pushes power levers. I'm really not sure if I can tell that the airplane behaves differently or if I just imagine it does because I know the forces are different. In the real airplanes which I've flown so far, I only really notice weight differences in slow flight, i.e. take off and landing, but the max and min weights are not so different. I try a steep turn at the lower weight and I nail it. Seriously, a HUD is the best invention since the windshield. This would so rock for aerobatics.

Insert a half second pause to consider what I just thought there. Okay, that's enough of a pause.

"Ladies and gentlemen, please ensure your seatbelts are fastened, your tray tables up and your carry on baggage securely stowed." I make a rolling gesture with my hand where Lee can see it but John can't, and he grins and nods. Look at the horizon. Look at the HUD. Coordinated aileron and rudder into the roll. Hold heading, hold altitude, hold the roll inputs, look at the horizon. Amazingly, it really feels like I've rolled inverted. You can actually see the ground ahead through the highest windows. Oh oh I shouldn't have swung my head like that. Check the nose, keep the roll going, look at the horizon, back to right side up, and roll wings level. I make a noise like "Yippee!" only less articulate. This is awesome. I'm sure someone who does a lot of aerobatics would be able to distinguish between the expected disorientation of being upside-down and the artificial orientation of a simulator asked to do something it can't sustain, but it felt good enough to me. Writing this, I realize I should have tried to sustain inverted flight to see how the simulator would respond to that and I might have tried it, but just then an alarm went off.

I look at the glareshield for an annunciator. I'm low on fuel, because that's what I asked for: minimum weight. John magically refuels me. "Inflight refuelling," I say, a standard instructor-in-simulator joke. And then I realize that this is an airplane that provides inflight refuelling to others in real life. I ask if we can simulate air-to-air refuelling. They tell me we need a flight engineer to do that right. In the J-model (we're in the Hercules C-130J) the Marines use the FE position as an FE, navigator, defensive systems operator, loadmaster and refuelling operations controller. Older models had more crew members, but automation has allowed them to condense the jobs. The FE is especially busy during refueling. the pilots just have to fly straight and level while the receiver hooks up and the FE does all the interesting stuff during the transfer. So while it would be cool to see the simulated receiving aircraft pull alongside, it wouldn't be any more educational than watching a movie of the real thing.

It really boggles my mind that they are pumping fuel between aircraft. I wonder if it's an aviator/aviatrix thing whether you see an aerial mating dance, or the comparatively little helicopters suckling at the teats of the mommy Hercules.

I'm trying to think of what else can I do in this airplane that I couldn't in any other. It has radar jamming countermeasures, but useful as that may be, it doesn't sound like a hoot to simulate, and it's the FE's job, anyway. "Can we drop the paratroopers?" I ask, "After the way I've been flying I'm sure they want out." Yes, the sim does do that. I often have to retrim an airplane because one person walked to the back. What is it be like when sixty-four of them jump out the back? There wasn't a crazy pitch change as John insta-fuelled me earlier, but that's not a normal function of the airplane, so I wouldn't expect it to be modelled. But the trainers would want a pilot to know what to expect when everyone jumps out the back.

I turn around so we're headed back to the airport, and we run the checklist. The pilot not flying, that's Lee, does the depressurization. Pressurization is so automatic that I haven't had to think about it yet, but the aircraft is pressurized, so popping the back door might not result in quite as orderly a jump as my simulated Marines have planned. Depressurization is trivial: he has set the pressurization control to "NO" and the rate of depressurization to "normal." It's easier to use than on the King Air. Our altitude (about 12,000', I forget) is good.

When the depressurization is complete, Lee tells me he's going to open the cargo doors and reaches up. Normal airplanes have separate panels for things like lights, fuel system and deicing. This one has all that, plus an 'aerial delivery control panel.' You can drop a tank out of this thing. I'm exercising bad CRM by rubbernecking at the panel and it bites me. The whole airplane shakes violently. I redirect my attention to the controls where it should be and manage the airplane. I have a caution light, but it's just the 'door open' light, not the 'door ripped violently from the airframe' light or the 'missile attack' light that it feels like. Apparently this turbulence is a bug in the sim: it's supposed to be simulating normal airframe vibration caused by opening the door, but every once in a while it produces too much vibration for the event. I slow to the jump speed of 120 kts. Lee is working more switches on the panel. Later I look and see that there are deflector shields (cargo bay doors and deflector shields (it's Star Trek: 2001), plus caution lights in the cargo bay so the jumpers know what is going on. Presumably I would have a jumpmaster or someone else down there to talk to on intercom, too. When Lee tells me everything is ready I "approve" the egress.

I concentrate on flying nice and level and not hurting any of my simulated jumpers, and try to feel if there is any simulated CG shift. Nothing significant. "How long does it take them to all exit?" I ask after a moment.

"They'd be out by now."

It was maybe thirty seconds. "Can I see them?" I immediately want to know, looking out the window. John doesn't know if the simulator shows that. I bank over and try to look, but we don't see any simulated parachutes opening. I'll just have to assume my guys (and gals, if there are there female paratroopers) are all alright. I head back to the airport while Lee closes the doors and tidies up after the jump. We totally abbreviated that procedure, and skipped a bunch of checklists required to ensure the safety of real jumpers. John sent me a lot of information on how it should have been done, so I'll post that in a later entry. Remind me if I don't.

Isn't that the coolest picture? It completely conveys "ready for anything" when you can jump out of an airplane wearing a parachute and swim fins. I guess they just jettison and abandon the parachutes, as you certainly couldn't swim with one. Seems a waste, but then I guess most military operations involve throwing something away.

I descend for the airport and join downwind. Lee talks me through it and sets flaps and gear. I feel like I'm flaring too early, but it's textbook, in the first third of the runway, on the centreline. As an instructor myself, I know that I can pretend to take credit for that, but it wouldn't have looked as nice without the unobtrusive coaching. On the go of the touch and go there's surprisingly little to do. No propeller levers, the gear is supposed to stay down for circuits (but I raised it after takeoff without thinking). I wouldn't have pilots practice circuits with the gear always down. You could train out the instinct to always check it, and end up with something like this.

There's not a lot of time for circuits. I want to try a bush pilot style short field landing, flare over the weeds and stall onto the beginning of the runway, so I fly a long downwind and turn base to set up a long approach, as I said before an easy way to help judge descent profile. But we have to be out of here with the sim shut down and ready for the next people by eight o' clock and it's almost time. Lee says, "Quick, let me show you something."

"You have control."

He takes it, cutting the corner to final and then he shoves the nose down, divebombing the airport. I think he might have added power. He overflies the runway without slowing down. And then reaching the other end of the runway, before I can say 'hey cool,' we're in a knife edge left bank. I look at the simulated ground, including radio towers and buildings. Just when I think he's about to roll it inverted, he cranks the yoke back the other way and makes an equally steep 270 to the right, pulling the throttle to almost idle. He calls for gear down and flap fifty, and before I have that set he has rolled out perfectly on the centreline and wants full flaps. Done, down and brake. I don't think we've quite stopped rolling when John shuts down the sim. Without the visuals, we can feel the pod resetting itself to the neutral position. I'm still saying "holy firetrucks!" or something like it as we unstrap, grab our stuff and vacate the machine with a couple of minutes to spare.

Apparently that roller coaster approach is a trick to confuse people who hang out near your airport with ground to air missiles, and aren't on your team. I won't be trying it soon in my ride. That was definitely more than a fifteen degree bank. It kinda violates the Transport Canada regulations on flying a circuit, too.

As we all left the sim building we passed the open door of a briefing room where two more clean-shaven young men in flight suits were sitting with an instructor preparing for their simulator session. I hope they do well, and what I've seen from the quality of the instruction around here, they will.

It turns out that Lee, whom I didn't get more than a handshake introduction to before flight, is working on qualifying to be an instructor pilot. I wish I'd known that before the session: I could have made better use of his knowledge. I tease him, "I'm an instructor. The first thing is you have to be more outspoken. Don't let some ignoramus in the left seat push you around when you know better." We chat for a bit about the airplane and instruction in general, but he declines my offer of beer and or dinner, probably seeing through my shallow ploy to siphon more information out of him before casting aside his lifeless husk. John watched me do that to an aquarium volunteer, probably warned Lee. Lee therefore accepts only my abject thanks for his role in my flight of fancy, and goes back to studying.

So remember if I flew the KC-130 simulator, and I'm not saying I did, because that could get someone in trouble, that's more or less the way of it. I might have got some things wrong or left some parts out. Those sinusoidal extraction fans are something else.

Afterwards John and I went to a generic sort of food place that unfortunately did not measure up to the barbecue recommendations some of you gave when I announced this trip. I had an unmemorable entree, but then one of the dessert items offered was deep fried cheesecake. If I tried the cheesecake, and I'm not saying I did, because that way it's symmetrical with the previous paragraph, my tastebuds were wary but ultimately happy, my pancreas seemed worried and my arteries cried out in anguish. Seriously, y'all will deep fry anything around here!

So, anyone else have any thrust levers or cheesecake I can sample?

Emergency Descent

I blogged recently about the panic engendered in passengers by the standard, safest response to a depressurization incident at altitude. I'll say it again, though. The one non-standard thing that has happened is that the cabin pressure has dropped. Passengers will feel this through ears "popping" and or pain in their sinuses and ears. They probably will not notice any shortness of breath.

Then the airplane and crew reacts according to design. The oxygen masks fall from the ceiling. Everyone screams. Drop them on the ground, with the wheels on the pavement, people still scream. The homey airlines like Southwest and Westjet will even include "stop screaming" as one of the instructed steps for use of the oxygen masks.

The crew begins an emergency descent. They are getting you and your screaming lungs to a place where you can breath unhindered just as fast as human reflexes, the surrounding terrain, and the structure of the airplane allow. The rapid descent is a good thing.

I can sympathize with passengers not knowing this, and even if they do know, I can understand how unsettling a rapid descent can be. And the pain can be very severe ruptured eardrums and sinuses do heal, however, while the results of oxygen deprivation don't. It's a very easy choice.

But the media are not sealed in a rapidly descending airplane with a crew who are too busy to make a passenger announcement about what is happening. They have the opportunity to ask questions of informed people. But they prefer to just talk to the shaken passengers. So you get things like this.

Up to 26 hospitalized in forced landing in France

The terminology "forced landing" usually refers to a landing made by an aircraft that cannot sustain flight, typically one without engine power. The descent to 10,000' was forced, but that's a whacky way to describe the event. The airline says that those taken to hospital were complaining of earache, and were all released. Judging from the line in the article, "Although French officials said the plane descended 26,200 feet (8,000 meters), Ryanair gave no details about a loss of altitude," the airline should take some blame for this ridiculous article because they didn't explain the emergency descent in their press release. The reporter is left believing that the airplane malfunctioned in some way so as to suddenly drop out of the sky, and has transmitted this ignorance to the readers.

26 Hospitalized After Ryanair Jet's Midair Plunge, Emergency Landing

Emergency landing is more accurate than forced landing, but really it was an emergency descent. I wonder if they even had equipment waiting. Once again the headline describes the response to the emergency, not the actual emergency itself. Is it because the actual emergency makes a boring headline or does FOX not get it either?

I'm not saying that the reason for the depressurization might not be a serious problem. I just want the media to realize that the rapid descent is a proper response to the problem, not the problem itself. If they did report that, then perhaps the next planeload of passengers to experience a deliberate emergency descent wouldn't think they were in a death plummet.

Fuel Inerting

While discussing the recent Qantas B747 incident with some very knowledgeable pilots I learned something that bears more research, about oxygen supply and fuel inerting technology. I'll start with some background and an overview of oxygen supply options in aircraft, before I finally get to the cool stuff that I learned.

The simplest way handle the problem of ensuring people on board can breathe is for the airplane to have an unpressurized cabin and non-turbocharged engines and to be operated only at altitudes where the engines and everyone on board has access to adequate oxygen in the outside air. Pretty much everyone who learns to fly does so in an airplane this simple. It works well. The laws of physics and of the government work in concert to forbid climb beyond a safe altitude.

The next method can be retrofitted into any aircraft, and that is to carry an oxygen cylinder and masks. Gaseous oxygen is compressed into the cylinder and the flow regulated by a valve. There are various mask and flowmeter technologies to ensure comfort and efficient use of the oxygen available, and you've read about some of the ones I've used. You can also have a similar oxygen system built in, which just means that the oxygen cylinder is stowed in a custom compartment, as opposed to in the cabin. Individual occupants attach their masks to outlets throughout the cabin. It has the advantage of being integrated with cockpit systems and seeming more sophisticated to the passengers, but the disadvantages that you can't easily take the cylinder somewhere to be filled and that you're married to masks that fit the outlets that were manufactured into your airplane at the time that Galaga was the pinnacle of videogame technology.

Remember that there IS oxygen at any altitude where airplanes fly, and it is present in the same proportions everywhere. You probably already know that air is 21% oxygen, 78% nitrogen and 1% other gases. we only actually need the oxygen to breathe, the rest could be replaced with something else harmless. So that proportion of oxygen stays the same as you go up, it's just that the air at altitude is at a lower pressure, so there is less of it in the same volume. One lungful of air at 18,000' has half as many oxygen molecules as the same lungful at sea level. If there were a way to cram more of that thin air into your lungs, you would have access to just as much oxygen as at sea level. And there is: pressurization. Under normal circumstances, most high altitude aircraft pressurize the fuselage to a breathable atmosphere. It's important to realize that this isn't a matter of sealing in ground level air and keeping it from escaping. The air in the airline cabin is constantly being replaced with air from the outside, it's just that it's compressed and cooled on the way in. A significant portion of a turbine engine is dedicated to compressing air, and there's enough left over, called bleed air to power some aircraft systems and pressurize the cabin. The airplane is fitted with outflow valves to prevent overpressurization. You can sometimes hear them making horrible whistling sounds. This explains why a small hole in the fuselage doesn't cause movie-style airliner disasters: there are already holes in the fuselage to let the air out. Adding another one might make the pressurization system work a little harder, but escaping air is replaced.

Sometimes, like on the Qantas flight I mentioned, something happens to create a bigger hole in the fuselage. The pressurization system can no longer keep up with the outflow, and the airplane depressurizes. The checklist in such a case calls pilots to don their own oxygen masks and commence an emergency descent. That means they cause the airplane to descend just as fast as it structurally can. Kind of a fun one to practice! Pressurized aircraft are required to have a supplemental oxygen system in place to allow everyone to breathe during the time it takes to descend from cruise altitude to ten thousand feet, where there is breathable pressure. In an airliner, pilot emergency oxygen is always supplied from oxygen bottles, as their masks are positive pressure, designed not just to increase the partial pressure of oxygen, but to exclude noxious substances like smoke. That's because pilots have to perform useful functions in an emergency, while passengers just have to stay alive. It's fair, really.

This is all extra scary for unknowing passengers because they witness the depressurization event, probably accompanied by a loud noise. The masks drop, which despite all the safety briefings still awaken some human fright instinct based on snakes dropping out of trees. The drop in cabin pressure is such that moisture in the air may condense into mist, which looks like smoke, and then the airplane plummets. Try to keep in mind, if this happens to you, that the plummeting is deliberate and for your own good. The masks really aren't designed to muffle your screams in order to maintain the concentration of the flight crew, (but I'm not saying that might not be a useful auxiliary function) so put them on and breathe normally.

Now, what are you breathing? In a Boeing 747 you're breathing out of an oxygen bottle, just like the pilots, just with a different mask. The airplane literally contains a big bank of oxygen bottles, bristling with valves and lines running all over the cabin to the passenger oxygen masks. As you breathe in wearing one of those masks you get some cabin air and some extra oxygen from the cylinders. Ironically, it was one of those oxygen cylinders, positioned in the nose of the aircraft, that caused the Qantas decompression in the first place.

On any other airliner, you are not breathing out of a bottle, but breathing oxygen custom made for you in response to your pulling the mask towards you, as directed in the passenger briefing. The compartment above your head contains a chemical oxygen generator, based around a compound that contains oxygen, in the same way that H₂O contains oxygen, but less stable. It takes a lot of energy to liberate oxygen from water, but just ignite something like sodium peroxide (Na₂O₂) and it starts to decompose. Na is elemental sodium, O is oxygen, and it takes two oxygen atoms to make oxygen gas (O₂). The sodium peroxide breaks down into sodium oxide (Na₂O) and releases oxygen gas. Here's the equation.

2 Na₂O₂ --> 2 Na₂O + O₂

You don't have to have understood high school chemistry to count that up and see that there are two Na atoms and 4 O atoms on each side of the equation, with nothing left over. Now, that's pretty neat if you can get around the bit I skimmed over and that is that in order to start this reaction, you set the oxygen generating chemical on fire. When you pull the mask briskly towards you, you are pulling a pin to fire an ignitor. You may even smell it burning. But despite the scary sounding implications, they are maintenance free devices. The only incident I know of where chemical oxygen generators caused a fire ValueJet where a number of the devices were being transported in the cargo hold, mistakenly labelled empty. They should have been deactivated for the flight. A real drawback of chemical oxygen generation is that it is a short lived system capable of putting out about 12 minutes of oxygen, just enough to get down to 10,000'. For flight in areas with a lot of high terrain, supplemental gaseous oxygen is required. Boeing offers this as an option on the B737NG and as a retrofit on other aircraft.

It would be nice to have oxygen available that didn't have to be held in either a pressurized container or an unstable chemical compound. And there is. In the air. There exists technology to separate nitrogen from oxygen in the ambient air. While the unpressurized air at 30,000' doesn't contain enough partial pressure of oxygen to sustain consciousness, the same pressure of close to 100% oxygen does. And the cool part is that generation of oxygen in this manner is just a side effect of fuel tank inerting.

See, when an airplane takes off, typically the tanks are full of fuel. In the absence of fuel tank inerting, as the fuel is burned, the resulting space (cool word alert: it's called the ullage) is filled by ambient temperature air and fuel vapour. Given the right conditions, this mixture of fuel vapour and air can ignite, to disastrous consequences. The idea behind fuel inerting is to fill the fuel tank ullage with something inert. Like nitrogen. And now if you didn't already, you see where this all comes together. During the flight, take the air that is already going by anyway, and make almost pure nitrogen, used to fill the unused space in the fuel tanks, and then have close to pure oxygen as a byproduct. I don't know much about the actual system that will be on the B787 Dreamliner, but apparently the whole apparatus weighs about as much as one passenger with luggage, and draws 40 kW of power.

The Boeing 787 will use this system. The B787 will also make a liar out of me for what I said about bleed air, but this post is about the fuel inerting. It's so symmetrically beneficial, it's almost as if putting my laundry in the washing machine somehow created both clean underwear and groceries.

Oxygen Service

I landed in Salt Lake City with 200 psi of oxygen left in my tank, so I called for oxygen service. I was cleaning out the airplane when they arrived with a cart full of long green oxygen tanks, so I got to see how this works. I showed them where the access was, a little door under the nose, and watched as they hooked up. I hopped up into the cockpit to watch the gauge, to ensure that it was filling properly.

I hadn't ever watched an O2 fill in progress before. I guess in my head I imagined them having a compressor, or one giant extremely high pressure oxygen tank from which they would charge my oxygen bottle. Or I never actually thought about it. But this being the real world, they have a collection of ordinary cylinders all at different pressures, and they fill by what they call a cascade. You can't ever get all the oxygen from one bottle to another, only equalize the pressure. So they start with the lowest pressure bottle that is at a higher pressure than my tank, and equalize the pressure between those two. Then they shut off the feed and switch to the next lowest bottle that still is at a higher pressure, and so on. They could just equalize my tank with the highest bottle in their array, but then what would they do with all the half-charged tanks?

Somewhere someone has a big compressor to fill their tanks. In case you're interested, an oxygen fill cost me $45 in Salt Lake City. Quite a bargain for about 25 hours of being able to breathe.

Darth Aviatrix

I mentioned my relationship with my oxygen mask. I have described before the nasal cannula method of supplementary oxygen, and trust me, having a drinking straw up each nose is preferable to having a plastic bag stuck over your face. I understand that if I stuck an ordinary plastic bag over my nose and mouth I would have passed out by now, so it must be supplying me with oxygen, but would anyone tell Transport Canada if I took the damned thing off and just breathed the rarefied mountain air? I wonder if this thing gives me force powers.

If I had blue skin, this is what I'd look like flying over the Colorado-Utah mountains wearing my oxygen mask. I don't really have blue skin: that would be a sign that I wasn't getting enough oxygen. (A co-worker tells me he once was on a flight with pilots who were trying to prove their manhood by flying over the Rockies without supplemental oxygen. he reports being unimpressed by their blue lips.) I don't know what vivid green hair is a sign of, but regular readers know that mine always comes out that way in posted pictures. Let me identify what you see on my head in the picture. The baseball cap (actually a feed cap) is dual function: the peak keeps the sun out of my eyes as I travel west in the evening or east in the morning and the headband serves to keep the sweat on my forehead from running down into my eyes. Sunglasses of course also protect my eyes from the glare, and also the high altitude ultraviolet. The headset protects my hearing from the constant noise of the engines and allows me to hear the radio, and the iPod when it's on. I left it off for most of this trip. Terri Clark wasn't working her usual magic on me. My nose and mouth are covered by the lovely and hated oxygen mask, held on with elastic straps, and in front of that you can see the boom mic from my headset, augmented by a light which I can control with my lip. Well, I can control with my lip when I'm not wearing an oxygen mask. The O2 mask has a rebreather bag, so you can gulp the same oxygen enough times to actually use it, and a tube connecting it to the oxygen supply in the ceiling. And of course there's my luxurious green hair.

I don't want to force this irritating contraption on others. In Canada, oxygen must be available to all passengers at pressure altitudes over 13,000', but the passengers are not required to use it. I check out the FARs to see what the local rules are. I must comply with whichever is the more conservative. It seems that in the US all persons must use oxygen for the entire period of flight above 15,000'. It looks like I brief everyone on oxygen, let them know it's available over 13,000' and then tell them to wear it over 15,000'. But I'm not going to turn around to check if they are complying.

Didn't They Expect This?

The TSA allows airline pilots to qualify as Federal Flight Deck Officers, undergoing selection and training to carry a loaded firearm in at their workplace. The program came into effect in 2003, as a response to the 2001 terrorist attacks using airliners. This past Mar 22nd, one of these guns was fired on the flight deck of an A319, puncturing the fuselage.

The result, as I'm sure has been explored in a Mythbusters episode, was that the airplane got a hole in the side. No one was sucked out, and the airplane did not explode. The plane was only at 8000', coincidentally the altitude to which the cabin was probably pressurized for most of the flight, so this can't count as a real life test of the Mythbusters' television show. The expectations of this entry's title are not, however, those of Adam and Jamie, but those of the TSA.

One of the lessons that aviation has learned well is that if something can go wrong, it will. It may take a long time, but eventually it will happen, and safety is all about being prepared for it to happen. Give thousands of pilots cups of coffee and some of them are going to spill coffee on themselves and the autopilot. (Hmm, maybe that's why my autopilots never work?) Give dozens (hundreds?) of pilots handguns and eventually one of them is going to accidentally fire it. Eventually one of them will accidentally shoot him or herself or another crew member, too. I wonder if any pilot has yet used his government-issued weapon to commit suicide. In Canada, eighty percent of gun deaths are suicides, and maybe five percent accidental, so I'd expect some suicides along with the accidents.

The TSA knew this when they resisted the FFDO program. I said that while I didn't think there was a huge risk posed by pilots having guns in the cockpit, that the risk from the guns was greater than the risk without the guns. Since 2003 I don't know of any US airplanes that had to be removed from service because of terrorist actions that would have been prevented by armed crews, nor do I know of any terrorist actions that were prevented by the presence of armed crews, but that doesn't mean there weren't any. The United States is pretty secretive these days.

There was no terrorist threat to this flight, and the discharge has been described as accidental, and tentatively as mishandling. Well, I'd think so. If a gun fires where and when it's not supposed to that would indicate poor manufacture, poor maintenance or poor handling. The expensive .40-caliber semiautomatic Heckler & Koch pistol was selected for the program as a gun that wasn't going to fire because it was dropped or subjected to turbulence, so either the pilot so abused the weapon that it was no longer safe, or he handled it in an unsafe manner. "An unsafe manner" here being a manner in which made it possible to be accidentally fired into his own airplane.

Apparently he was stowing the gun in preparation for landing. Now anyone who knows the details of the FFDO program is not allowed to disclose them, but I don't know anything about it that isn't posted on the website, so I'm free to speculate. As the gun is approved for a particular pilot, clearly the gun comes on board with the pilot at the beginning of his workday. So either the pilot carries the weapon through the airport and through security, himself or some secure designate does, and gives the weapon to the pilot at the airplane. The latter seems weird and needlessly complicated: the pilot would have to check in, find the designated person to carry his weapon to the airplane for him, and then rendezvous with that person on the airside. It would be a pain in the neck. So maybe that's how it works. Either way, once the pilot is on board the airplane he has his weapon. Now did it come through the terminal loaded or unloaded? Either he loads it at home right after putting on his tie, and then carries it, loaded and holstered, right through his day, or he carries it through security unloaded and then loads it in the airplane.

Loading it at the beginning of the day means less handling throughout the day, but also that the gun is loaded at times when it is not needed to be ready. Loading it on the flight deck might require loading and unloading several times during the day, as the pilot changes airplanes during one duty period. I would be willing to believe either strategy, perhaps leaning towards 'loaded all day' because otherwise they'd be standing in the galley loading their guns, so as not to be seen by people staring at them through the windows of the terminal. (I once had an airline pilot come up and speak to me reassuringly, because he'd recognized me as the one who'd had her nose pressed to the glass watching, and mistaken my "I wonder if I'll make it" expression as one of apprehension about the flight rather than hope about my career).

Whether the gun comes on board in a case or a holster, it has to be accessible during the flight, or there is no point in it's being there. I would think that a shoulder holster would be a natural place to keep it. Amusing as it would be, it doesn't make much sense to slap it down on the centre console: it could slide off and end up under the rudder pedals or seats. Unless A319s have been modified to include a dashboard gun mount, there's no secure but accessible place to put it down.

I'm guessing that the pilot in question did find some place to put the gun that he felt was a better compromise between secure and accessible in cruise. The turbulence and movement associated with descent and landing was such that he intended to return it to its holster before landing. Perhaps he picked up the gun in a way that allowed his finger to put weight on the trigger, or almost dropped it and grabbed at it, causing the discharge. I don't want to believe he was playing with it.

I am certain that there is not a single control in an airplane that some commercial pilot has not accidentally mishandled. If you retract the gear instead of the flaps, it's embarrassing and expensive. If you mishandle manual pressurization it's painful. If you make a PA on an ATC frequency it's embarrassing. I still don't think that the risk of not having guns is worth the risk of having them, but perversely, I'd probably apply for the FFDO program if I were eligible. But I wouldn't be handling my gun at 8000' unless I perceived an imminent threat of the sort that can be countered with a gun.

The comments on this issue are by definition amusingly uninformed, because anyone who knows enough to comment in an informed way is bound by law not to disclose what he knows.