Saturday, December 06, 2008

Two Settings

The weather associated with the warm front has passed and a cold front is expected tomorrow. The customer calls me in the afternoon to go and do some flying. While I am preparing the airplane for takeoff, my replacement arrives at the airport. He appears around the hangar from the airside. I assume he disembarked through the terminal and then reaccessed the airside at the FBO, as opposed to hopping off the airliner and strolling down the apron. Procedures at this airport aren't that lax.

It's good to see him. I arrange to meet him again the next morning for a handover briefing. The best time will be at 6 am before he has to meet with the customers. It will mean only four or five hours sleep for me, as I expect to land around midnight and not be in bed for an hour or so after that, but tomorrow is not a duty day for me and I can try and sleep on the airline, and then go home and sleep for real. Any alternative would either delay this flight or delay his duty rest tonight. He's been on airplanes all day to get here.

There's only a little bit of light left in the sky by the time I take off. I probably didn't log it as a night takeoff, but I probably didn't log it as a night landing, either. I always forget. I probably have hundreds of hours of night flying logged as day flying in my logbook. It will get a lot colder as the night goes on, and there may be some mist, too. During the day you barely need the heater while the outside air temperature is above -10C because the bodies inside keep it pretty warm and the sun seems to come in the windows better than it goes out. Flying greenhouse. I have the heater turned on now, but on low. The outside air temperature is -4C, just below freezing. I don't have a thermometer showing inside, but I'm comfortable sitting in a sweater.

It gets a bit darker and a bit colder and after an hour or so I'm asked for some more heat in the back. "Coming right up!" I move the temperature selector placebo lever to the right. Not all the way to the right, because if you turn this heater to full there's a chance that the overtemp detector will cut in and pop the circuit breaker before the heater cycles off on its own. That might not sound so bad, except that the CB for the heater is not accessible from the cockpit, nor from anywhere inside the airplane. You can't reset it until after landing. It's meant to be a failsafe against cold pilots desperate for heat if the heater really is malfunctioning. Too bad they couldn't have done it with a self-resetting thermocouple of some sort, but seeing as the heater is a drum in the nose, just forward of my feet that is literally burning gasoline, overcaution is a good thing. Another name for these heaters is "nose bombs."

About fifteen minutes later it's still too cold in the back. I tweak the lever over further, and turn the heater switch off and on again. Perhaps the heater cycled off and didn't restart for some reason. The weird thing is that there's two heaters, one in the front and one in the back, so can they both have died? When I have passengers I've been running the back one from takeoff in the cold, and then turning on the front one when I get cold or when they ask for more heat, but I now suspect that the back one hasn't really been working. I can't test it on the ground, because you're not allowed to run it on the ground: there is insufficient cooling.

It's still getting colder in the back. Damnit! I let them know that I am sorry, that I am doing all I can to heat it up, and that I am personally willing to continue. Paranoia (pilots call it "safety concerns") drives me to dress for every flight as if I am going to have to spend the night in the wilderness. So it's not unsafe for me to fly without a heater, and my airplane is sufficiently old-fashioned enough that freezing temperatures don't affect the essential flight instruments. If the flight is to be discontinued, it is their call.

And they call it. Their computers aren't tolerating the still-dropping temperatures so I head back to land. I don't know what is wrong with the heater, but I don't try to troubleshoot in the dark.

I clean up the cockpit and make sure I've left all the charts and airplane specific equipment. I pack everything that is my equipment into my flightbag and neaten up the seatbelts and so on, so it will look nice for my co-worker in the morning.

He's still up, so I head by his room and debrief there. I fill him in on the customer expectations, the FBO hours, the telephone number that is supposed to summon deicing, and the restaurants to avoid. I give him the logbooks and other paperwork. And I tell him apologetically about the heater situation I have left for him. "With luck, it's just a circuit breaker," I suggest hopefully. He asks if the heater was on high. I shake my head. He knows how it works too, so neither of us is very confident that a circuit breaker will fix the problem. "There's a good chance, though," I confess, "that when you turn it on it will just work. I seem to have psychological influence over airplanes. And I really wanted to go home more than I wanted to fly tonight." He doesn't even laugh. He's seen enough capricious airplane behaviour not to blink at it.

I really have seen such behaviour but there are more rational explanations than a pilot's subconscious mind having the power to suppress electrical circuits and bend metal. Things go wrong with airplanes all the time. It's the nature of the beast. This is just a matter of when and where we notice them and recall them. Firstly, a pilot who really would rather not fly today is more likely to notice and respond correctly to an indication that something is not right. A pilot who really wants to get the hell out of an Indian reservation in the middle of nowhere is very unlikely to notice a broken MP gauge before takeoff. So the defect will go unnoticed there and will instead show up when the pilot is home at the maintenance base, or somewhere else the pilot doesn't mind being stuck. And secondly, when the defect is noticed, if it's something that delays the pilot but has no other particular impact, it's not long remembered. There are many causes of delay and thy happen all the time. But when the defect spares the pilot from having to make a flight she didn't really want to do anyway, it takes on more import, and is longer remembered. I imagine that there is some correlation between pilot morale and "ramp rash" too. Pilots like to be in control, so claiming psychokinetic responsibility for things we have no control over is right up our alley.

In the morning the heater does start up flawlessly. It wasn't the power of my subconscious mind, however. When we consult the mechanic about it he asks what was the outside air temperature, what was the humidity like, and what was the heater setting. That the answers are respectively "just below freezing," "some visible moisture," and "low" solves the mystery. Set to low, the heater runs for a while then shuts off and lets the temperature drop. With the outside temperature -4C and not -20C the airplane cools slowly, so the off cycle lasts for several minutes. During cooling the pitot tube-like air intake is collecting moisture, which freezes and blocks the intake. And then the heater cannot restart.

So not only does out heater have the traditional two settings "too hot" and "off," but those two settings are too hot and leave it on for the whole flight or else versus off for the rest of the flight. You can't win. But at least I can go home.

5 comments:

dpierce said...

Your heater has a lot of rules. I can tolerate quite a bit of discomfort, but being cold is miserable, and it must've gotten awfully cold for computer equipment to act up. (If that wasn't an excuse :-D )

Other than a sweater, what sort of survival gear do you carry? And do you consider it a required loading, or are you willing to part with some of it for weight considerations?

Aviatrix said...

Your heater has a lot of rules.
Ain't that the truth. But then everything does. There barely a control on the airplane that doesn't have limits on the settings and phase of flight at which it can be used. In a car (or an Airbus) there would be interlocks or other mechanisms that made it impossible to set things to the wrong combinations, but in this aircraft 'm trusted to get it right myself.

It must've gotten awfully cold for computer equipment to act up.

I think it has to be kept above 5 degrees.

Other than a sweater, what sort of survival gear do you carry?

Parkas and a sealed survival kit. I'll have to do a post on that. The survival box doesn't really weigh enough to make it a consideration in what to leave behind. It's probably five minutes worth of fuel. We're not in Australia so we carry water purification tablets not actual water. I take on a separate supply of water for desert flights.

matical said...

I've been working on a survival kit suitable for the mountains and back-country in western Canada - and a flotation device. (Did you see the news report of the Mooney that ditched north of Vancouver yesterday?) ...

Any thoughts and experience you have on those topics would be of great interest.

Sarah said...

Only -4C ? Sounds like the problem of being too warm will solve itself once winter develops. In my little airplane, the "heater" is left full-on all winter and it sometimes struggles to warm the cabin air to -4C. It's past time to buy the chemical boot heater inserts again. Heater and sun warms everything reasonably but my feet which are blocks of ice after about an hour.

Things go wrong with airplanes all the time? Small things. And (good) pilots are always on their guard. What was that noise? Does that sound different? Oh, we're just over un-landable terrain, that engine always sounds like that then. :)

And sometimes you're right, but the defect is "acceptable". The fuel pressure drops to 2psi momentarily when boost is shutoff? That's just the engine-driven pump unseating it's check valve.. don't worry unless it doesn't recover in a few seconds. There is a notable vibration at 2000 rpm? That's ok - the prop needs dynamic balancing after it's last nick removal polishing. Don't use 2000 rpm.

I guess the trick is to learn what matters and what doesn't. I'm learning...

zb said...

Hmmm... "sleep on the airline?"

While this may sound weird, technically, if taken in a very strict way, it does help towards perfect clarification in the sense of you not sleeping while being on the controls yourself, flying.