Saturday, November 19, 2005

Thump Thump Silence Thump

You're going to think that I fly poorly maintained airplanes, but I don't, really. We have well-paid maintenance whose word is law when it comes to acceptable parts and standards. A Transport Canada auditor said that he wished all companies met our standards. But just as fit athletes sometimes get sick, well-maintained airplanes sometimes malfuntion.

We're flying along, minding our own business, and a red light comes on on the dashboard. It's not the friendly blinking interrogation light of the transponder, occasionally frightening to passengers, but really just assuring us that ATC radar is reaching us, and that our airplane is answering back with its proper code and altitude. It's the gear transit light. The one that comes on in between moving the gear handle to a new postion, and having all three wheels either down and locked, or neatly stowed inside the airframe. And that's odd, because the gear has been up since just after take-off, and that's where we wanted it.

It's not that odd, though, because it turns out that the gear is transiting. A moment later there is a thump, and immediately afterwards a second one. But no third one. We now have three lights: a green one for the right main, a green one for the nosewheel, and a red one indicating an unsafe gear state. I know that with the gear extended and the gear handle in the up position, a motor will run continuously, so I ensure that the aircraft is below gear extension speed and select gear down. We still have only two green lights. I consider how much damage would be done to the airplane and company reputation by a landing rollout that occurs on two wheels and a wingtip. This wasn't in my plans for tonight. But after the airplane discovers that it can't scare me, it deigns to release the third wheel.

We check to ensure that the emergency release hasn't accidentally been pulled, and then we slow the airplane further and attempt to raise the gear. This isn't tempting fate as badly as it sounds: it is pretty much a gravity-driven extension system. Hydraulic pressure in the system holds the gear up. An electric motor maintains hydraulic pressure, and switches surpress the motor when the gear has finished a transit, so that the motor doesn't run continuously. The deployment is likely caused by a leak in the hydraulic system, but maybe it's a slow leak and the gear will stay up for a while more. But nothing happens. I don't want the motor to run continuously and burn out or cause a fire, so I select the gear down again and it stays down. No surprises there.

Landing uneventful. Comments from colleagues regarding "better stuck down than up" as predictable as the "doing mine next?" comments you get whenever you wash your car. Journey log annotated with the complaint. And that's the end of my day.


Anonymous said...

Ahhh. Cold weather and hydraulic leaks. Don'tcha just love Canadian winters?

Anonymous said...

Did you guys pull out the checklist? Why would you try to select it up? What if it didn't come down again?

Aviatrix said...

We don't have an uncommanded gear extension checklist nor a gear-fails to-retract checklist, so no.

I know how the system works, and the issues that would cause the gear to not retract do not affect its ability to extend again. I didn't have a lot of hope that it would come up, and less that it would stay up, but it was worth a try. Leaving the gear extended increases our fuel burn per mile, and decreases our cruise speed.