Post Mortem

Well what a clusterfailure that was. Imagine if that vacuum and indication failure had all happened over the course of once turbulent flight in night IMC across the mountains. Suction failures are extremely dangerous. The suction-driven instruments are central to the instrument scan and experiments and studies of actual accidents show that they have a very high chance of killing you. The "ninety percent" figure sometimes quoted is misleading: accidents attributed to vacuum failures (about three per year in the US) result in fatalities 90% of the time. That's because there aren't many ways to crash an airplane due to spatial disorientation without it being deadly. More than ten percent of pilots who experience vacuum failure in IMC do get out alive, but I'm not going to guarantee I would be one of the survivors.

Here's what a vacuum failure can look like.

The gyrating blue and black instrument is the attitude indicator. It won't necessarily look that energetic in a failure. Its slide to one side or the other may look exactly like a functional instrument indicating a real wing drop, prompting the pilot to bank and pitch in an attempt to return the aircraft to straight and level flight. The pilot must fly by the turn coordinator, the tippy little white symbolic airplane at bottom left. It indicates rate of turn, not bank angle, so doesn't respond as instantaneously to changes in attitude.

I had difficulty identifying the failed vacuum system because its own indication system did not work properly. When I felt that the heading indicator was not working properly, I suspected the vacuum system, but the indicator lied to me, telling me the system was okay. When I shut down an engine, the associated vacuum failure indication appears immediately, leading me to believe that the same thing would happen in the case of a real suction failure. The two vacuum pumps are in two different engines, had widely separated serial numbers and had been installed by different people at different times. I had never heard of one vacuum pump failing and taking out another one.

If an electric instrument has a power loss, it immediately throws up a flag, so I know not to trust it. There is no failure indicator on the heading indicator or attitude indicator and without other reference, it is really easy to follow the dying instrument. The autopilot tried to follow it, too. With TWO failing vacuum pumps, there was no pressure differential across the shuttle valve to pull the autopilot out of the system. Flying across the mountains to the FBO where company has shipped the replacement pumps, I have post-it notes over the failed instruments, still the only indication, apart from their unresponsiveness, that they are not working. When practicing flying on instruments, if the pilot can see the real horizon, even a little, the task is much easier. Even if you try to ignore it, you subconsciously draw on a lifetime of doing what your species does: visually determining which way up you are. While it's easy to design an indicator that is invisible until electrical power is removed from it, I guess it's harder to calibrate one to not enough suction. Maybe it could depend on gyro rpm. This FAA document claims that "attitude indicators with failure warning flags are available in newer model aircraft and are slowly making their way into the general aviation fleet as retrofits," but I think they may be talking about replacing vacuum-driven AIs with electric ones.

The cause of the double failure is eventually determined to be poorly-installed air-oil separators. Oil was able to enter the dry vacuum pumps and damage the vanes. I'm not sure if the indication issue was because it was a gradual failure, or because oil got in the indicator, too. It is all functional now, but now the vacuum pumps are in phase, which makes me nervous, because that airplane has flown about 900 hours since that happened, and I'm back in it. This article seems to think that vacuum pumps fail every 500 hours or so, but our mandated time between overhaul is definitely 1000 h.

Are there one or two Ns in "Brokenness"?

I start the engines the next day to do some VFR work. As the engines fire up, the engine start checklist directs my eyes to the tachometer, then the oil pressure, and to the suction gauge. The suction gauge indicates that the right vacuum pump has died. Okay! That sort of explains the zombie heading indicator, and means that I've snagged the wrong instrument. I should have not written it up while it was questionable. The laws don't allow me to write, "never mind, it's not broken after all," which is why there are so many airplanes flying around with sort of broken stuff. As soon as it's written down, it grounds or restricts the airplane. As I understand it, only a maintenance engineer is allowed to correct a pilot's mistaken snags.

Fortunately, the effect of the unserviceability is the same, as I'm not allowed to conduct IFR flights with only one vacuum pump working, and we're in the north in the summer, so "night" is virtually non-existent. What's weird, though, is that the reason there are two vacuum pumps, is that one is supposed to be able to serve as a back up. Either suction pump on its own is supposed to be sufficient to run both the attitude indicator and heading indicator. I'm supposed to be able to safely complete an IFR flight with one suction pump failed. Come to think of it, the autopilot is not supposed to engage if only one vacuum pump is operating, to ensure that there is sufficient suction to run the essential instruments. The autopilot is still working, although a little half-heartedly, as the heading indicator is still sluggish. So is the attitude indicator. The shuttle valve that is supposed to disable the autopilot must have failed, so the autopilot is remaining on line, leaving not enough suction for the heading indicator and attitude indicator. I turn off the autopilot, but it doesn't help much.

After a few hours the heading indicator and attitude indicator are both completely useless. Weirdly, the autopilot will still engage. (I keep forgetting and snapping it on when I want to look something up or open a Clif Bar to eat). But it will attempt to follow the slowly toppling attitude indicator. Pretty scary, really. How far would it roll the airplane? That's not in the manual.

In the old days, there were no heading indicators or attitude indicators or autopilots. The turn and bank instrument and the compass were all you had for staying right side up, and if the former died, it was just the compass, which has all kinds of errors or lag and lead. The old bush pilot trick for letting down through an overcast was to do so on a heading of south. On south, if you bank at all, the compass will immediately swing around, even before the heading has changed, especially at high latitudes. I try this at the end of the flight, because my destination is pretty close to due south of my position. It's pretty hard. Try it sometime.

As I taxi in at the end of the flight the suction gauge indicates that the second vacuum pump has failed. Well this would make a fair amount of sense: the pressure differential between the working and failed vacuum pumps is what is supposed to throw the shuttle valve to disconnect the autopilot. And obviously if they have both failed I can't expect the suction instruments to work properly.

Company has already made arrangements to ship a vacuum pump to a maintenance shop a few hours flight away, so now they will ships two vacuum pumps, and we will head there on the next flight.

Getting My GPS Fix

As I searched my bookshelves for a book I needed to prepare for my PPC, I realized that I have been incredibly remiss in not devoting a blog entry to my favourite GPS book, Max Trescott's GPS and WAAS Instrument Flying Handbook. It is dog-eared and filled with notes on the multiple ideas for future blog entries it inspired. Max There are two reasons this entry never has never been written. One is that I had this crazy idea that I was going to be able to fully digest all the information in this book, and then write the mother of all blog entries on GPS, and the second reason is that when I pick it up it's usually because I have to learn something, and get carried away with that.

Today is one of the latter occasions, and I've given myself a time deadline to study this, so I'm just going to transcribe some of the marginal notes I made reading through the opening chapters. "Excellent and now obvious," "Max knows what he is talking about, doesn't just parrot, which explains why I am not understanding things I didn't before." "Explains from zero knowledge without insulting intelligence."

There's lots of information on GPS on the Internet, but my time is worth something in sifting the wheat from the chaff. The Internet seems to be at odds over whether the unit can be programmed to fly a hold. Given that none of the Internet people I saw say it could be done gave useful step-by-step directions on how to do it, I was believing the naysayers, but Max says, "The Garmin GNS 430W and 530W send commands that let an autopilot automatically fly a procedure turn or a course reversal in a holding pattern. On the moving map page, it adjusts the size and shape of holding patterns based on an aircraft's speed and the winds aloft. Once established in a hold, it can command the autopilot to fly the holding pattern as long as you'd like." And now I see that the unit will only do this for published holds. Max does give some tips, some credited to a colleague, Doug Stewart, on flying unpublished holds. I'll reproduce them here to enhance my understanding and remembering.

The typical hold clearance (a "hold" is the way an air traffic control asks a pilot in an aircraft that requires speed in order to stay aloft to "go wait over there for a bit") instructs the pilot to fly directly from her present position to a specified point (called a "fix"). The fix can be any defined point in space, like "thirteen miles from the ABC VOR on a bearing of 298 degrees" but usually it's a VOR or an NDB. The clearance then includes a vague direction (north, east, southwest) from the fix to hold and an exact track on which to be inbound to the fix each time she circles around. The goal is to fly a little racetrack pattern, with each inbound leg taking exactly one minute and being right on the specified track. The outbound leg isn't necessarily parallel or one minute, because winds mess us up. What also messes me up is trying to learn a procedure I use once a year when I renew my qualifications. But if I master this I can probably also use it to fly shuttle climbs and descents, which I do use in real life.

So here is what I should do: Once assigned the holding fix I set the course direct to it, with the autopilot in NAV mode to track to it. Once the autopilot has figured out the heading that will hold me on that course, I should bug that heading and fly in HDG mode on the autopilot, while I set up the hold. I hit direct to again on the autopilot and enter the inbound course as the desired track. That makes it show a pink line to the fix along that track. I should put it in OBS mode so it doesn't automatically go on to the next waypoint. Reaching the fix, I turn the heading bug to my calculated outbound heading. When I have flown outbound for the necessary time I should use the heading bug to turn inbound, but when I am within 45 degrees of the desired inbound track, I turn the autopilot back to NAV and it will intercept and track inbound. In a direct entry, I can use the ETE feature of the GPS to figure out my timing, by looking at the distance when it hits one minute, and I can look at the wind correction to figure out my outbound correction angle. Curiously he suggests triple the inbound correction, while I use double.

I see Max Trescott also sells a CD ROM course for $100. Given that that's the cost of about twenty minutes of dual instruction in a light twin, I suspect it would be worth one's while.

Logical Deductions 101

This post might have followed this post had I blogged things in the order of the notes I made for you. See, I still make notes for you. I make them right on my OFP, my operational flight plan, an official document of sorts which my company has to keep on file for years, or at least months, I don't feel like remembering which. It (this post) still follows it (the other post). There are just intervening things. That's what life's like.

In that post, which was mostly about canola, we had to backtrack a runway, and make other traffic wait for us, after landing despite what appeared to be a perfectly serviceable crossing runway that led back to the taxiway. The other runway was closed. Now for the exciting conclusion.

The next day on preflight inspection I find grass clippings on my aircraft. (Disclaimer, they could have been canola clippings). This isn't completely bizarre. In the last month I have found things as diverse as mouse intestines, dime-sized purple blobs, and fluffy weed seeds on my airplane. I suspect a messy owl dining atop my vertical stab, birds that had previously eaten purple berries, and fluffy weeds, respectively. The last one really doesn't require much in the way of logical deductions, but it still needed cleaning off.

I start up and I listen to the ATIS, which tells me that that the other runway is closed now and the previously closed one is open. There wasn't anything wrong with the one I landed on yesterday, and if they were painting or sealing or something they'd be smart enough not to mow, wouldn't they? It turns out the runway is closed for mowing. They need to close the whole runway for mowing?  It's a paved runway. They don't have to mow the runway itself. I'll bet I have landed more than a hundred times at airports with only one runway, while mowing was occurring. Sometimes there's an elaborate procedure whereby the controller advises the people with the tractors to remain clear of the runway. Sometimes they just publish a NOTAM or say on the ATIS that mowing is in progress. And sometimes you're on short final and it's like "SURPRISE! TRACTOR!" crossing the clearway. But we're pilots. We deal with these things. But that's not apparently how you do it when you have two runways.

The airport is busy. Lots of landing and departing traffic and there's a Nav Canada Challenger jet flying dozens of passes from different directions. I hear they are planning a new RNAV approach into here. I did the DME/LOC the other day, testing the autopilot, and it was pretty usable. You come over a wide canyon on the way in, so no obstacles letting the designers give you a low enough MDA that I had my hands very right there, should the autopilot decide at any moment that now would be a good time to dive. It didn't.

Also my coworker has brought five separate pairs of footwear. I have one: I fly, go to dinner and work out in the same shoes. So why does his luggage weigh so much less than mine?

Over the Airwaves

I know I haven't updated in a while, but I'm very busy working, among other things. Here's today's flight.

Breakfast and paperwork all on top of one another in the hotel, to file two flight plans covering nine hours of flying over the day. They are somewhat specialized plans, so have to be faxed in to the IFR data centre at least an hour before take-off, so they can process them. We can do a turn in thirty minutes--we measure that touchdown to wheels up, so we taxi clear of the runway, cool the turbos, fuel, pee, refill water bottles, clean the windshield, restart, taxi out and roll again all in less than half an hour, our record is twenty-seven minutes, so the second plan has to be filed before we land the first flight.

Airport shuttle, fuel in the morning, to get cool fuel and fuller fuel tanks, then start up and call for clearance. I'm at an airport served by a Flight Service Station, so I call them, identifying my aircraft by callsign, type and position on the field plus the fact that I'm "looking for IFR to Moose Eddy." He gives me active runway, winds and altimeter setting, and then says nothing else. I call back and ask if I get my clearance from Centre, but he doesn't reply. I take this as a sign he's on the phone to Centre and figure he'll come back with my clearance in a bit. He does. It's a long one, with a crossing restriction and a "not valid if not airborne by" time, details usually absent from northern clearances. I read it back and punch in the transponder code.

I go on with my checklists. Airplane is running great lately. Apparently the magnetos are due for overhaul in under 25 hours, they're on extension already, but they all seem to be running well. The engines start well, run smoothly and the magneto drops are well within the acceptable range. We had a problem with the right engine fuel injectors a while ago: they kept clogging, so we replaced the fuel servo (turned out it had some corrosion that could have been a source of the clogging matter) and also upgraded the injectors. I believe we replaced the left fuel servo too. When everything checks out and the engine temperatures are nice and warm I taxi out and take off, with three minutes to spare on my clearance valid time. Given that my clearance valid time was my filed departure time, they didn't give me a big margin.

The FSS guy says to contact Centre through 5000', which is my crossing restriction altitude, cross 20 DME on course not above 5000'. The trick here is to get in touch with Centre and then they'll lift the restriction, so I climb quickly to 5000' and sure enough the crossing restriction is lifted and I'm cleared to my requested altitude en route. The controller says, "Contact me reaching," and then stops. I pause, waiting to see if he'll add reaching what, but he doesn't, so I read it back as "reaching one three thousand." I heard someone else get a similar fill-in-the-blank clearance here a few days ago. Must be the local dialect. It's amusing how something as aggressively standardized as ATC develops dialects. It demonstrates how easily Latin disintegrated into all the separate Romance languages as soon as it no longer had an army to back it up.

A good tailwind gets us where we're going in an hour, but conditions are not conducive to the work we're here to do, so we turn around and go home. I tell ATC why, referring to "the required quality" of our data. There's another company out doing the same work and my words may have shamed them, as I hear them quit ting too, shortly after we turn tail. We have a headwind going home, so it takes an hour and a half to get back even though our speed is aided by a 15,000' descent (don't worry, no underground stuff: we climbed higher than that initial clearance as we approached the work area). I pass the time listening to my iPod. But not music: Italian lessons. Oh yes, that earlier reference to European linguistic diversity was apropos of something. The differences from Spanish and French are so cool. Verb endings... how the hell to verb endings evolve in a language? It makes me understand how people can deny species evolution. The ability of time and tiny changes to effect big changes is hard to wrap ones mind around. I'm learning Italian because I'm going to Italy, and I you know I can't survive long without the ability to talk to people. Se parleresti italiano, scrivimi! Se potresti Skype posso cercare parlare.

My boss is planning to do a PPC in this airplane this month, so I test the autopilot on the VOR/DME approach. It works okay, but the descent rate it selects is proportionate to the altitude change, so when I ask it to go from 6500' to the 25 nm safe distance it plunges so rapidly that it sets off the terrain warning. It takes its time aligning properly with the runway, and level eight miles final at the no procedure turn altitude the GPS is going crazy with "terrain" and "too low" (I don't even remember seeing that last one before). I take control from the autopilot when I want to put approach flaps down, because the manual says not to operate it with any flaps extended. That seems kinda dumb: what's the point of having an autopilot that can capture a glideslope if it can't do it with flaps? I wouldn't want to have to reconfigure this airplane from clean to landing configuration at decision height. A previous autopilot I used required me to disengage it while extending flaps, which made more sense. (Hand flying makes it easier to immediately recognize asymmetric or runaway flap conditions).

Land and roll out. On the backtrack the FSS guy asks me if I was IFR for the last part. Wha? I specifically told him I had cancelled IFR and that I was going to fly a simulated approach to test the autopilot. I didn't have to tell him that, but I apparently I care enough about what controllers think about me that I wanted him to not consider me an idiot if the autopilot wandered off somewhere and I waited to see if it would figure it out. There was quite a strong crosswind. I can track a radial better than it can. Yes! I'm superior to a thirty-something year old machine! We take our joy where we can.

I taxi clear of the runway and call off with no acknowledgement.  A helicopter pilot starting up on the ground makes two attempts to raise the FSS guy and then calls me to check his radio. I tell him FSS guy is probably on the phone. FSS guy comes back and apologizes, "There was a kerfuffle at Squirrel Inlet."  He's looking after traffic at a different airport as well. The helicopter guy hopes everyone is alright and the FSS guy says yes, just a lot of traffic at once.

And then we shut down and got a cab. Too early to check into the hotel, so I'm blogging in the lobby.

Oh and don't worry, I remembered to cancel the second flight plan.