A STUCK THROTTLE
By, Captain Nancy Aldrich
Today I am writing about one of my personal experiences. I try to avoid doing this because many of you have read my book and I do not want you to have to re-read a story you have already read. However, this story is not in my book, so I hope you find it interesting and amusing.
I have frequently been asked if I have ever been afraid while flying, and I can truthfully answer, ‘no.’ However, there have been many times that had my full attention. I was working hard and thinking hard, and I might even have been a little shaky once safely on the ground. In the air, I was too busy flying the airplane and solving the problem to think about being afraid. The fact is, pilots are very well trained to handled every conceivable problem that might arise. And, problems do occasionally arise.
The training is extensive (and intensive!), and I remember that as an instructor on the DC-10, we would sit around and try to think up “what if” scenarios. We wanted our pilots to be trained to handle anything.
Many people seem to think that if the engines quit on a passenger airplane it would crash. One of the exercises we did in the simulators was to shut down all the engines, and put the plane 30 miles away from the airport and 10,000 above the airport and tell the pilots in training to land the airplane. No one had a problem doing that. (Most passenger airplanes are very good gliders, and have a glide ratio around 18 or 20 / 1. That means that the airplane will glide 18 or 20 miles for every mile it descends. Most passenger airplanes cruise between 8 and 10 miles high, so they can glide a very long distance!)
The point is we are trained to handled all situations we might have to face, so when there is a problem, there is no reason to be afraid, we just get busy and handle the problem.
Having said that, there are some unusual situations. One stormy afternoon, when I was an Engineer on the DC-10, we pushed back from the gate in Chicago on our way to Seattle. Because of numerous thunderstorms in the area, we parked the airplane and waited for about 45 minutes, in heavy rain. Believe it or not, no passenger planes intentionally fly through thunderstorms! Finally, the weather was good enough and we rolled down the runway and headed to Seattle. In was a pretty routine and uneventful flight.
As the Engineer, it was my responsibility,about half way through the flight, to send the engine data to the company. In order to get accurate readings of all the parameters, I would click off the autothrottles and set the engines to an equal fuel flow. As I was doing this it became apparent, I could not move the center throttle. The Captain and First Officer noticed my struggling and offered to set the throttles for me. They could not move the center throttle either. As we discussed the problem, we decided it must have had something to do with the rain, and the -35 degree temperature at altitude. I sent the information for the #1 and #3 engines along with a note that the center (#2) throttle seemed to be frozen.
As we approached Seattle, the Captain made the decision to descend early to give the throttle time to thaw before landing. About 100 miles prior to landing, we descended to 10,000 feet. It then became clear that the throttle still would not move and we could not slow the airplane below 300 knots. Landing at 300 knots was not an option! It was obvious that the engine would have to be shut down. Being responsible pilots, we got out the book and followed the “Engine Shut Down In Flight” checklist. Of course, one step in that checklist is to move the throttle to the idle position – we could not do that. However, shutting down the engine did give us control over the speed and we could slow to an appropriate speed for landing.
Because we were in an unusual situation, landing with an engine shut down, we had the Flight Attendants prepare the passengers for an emergency. We were quite confident there would be no problem, but the regulations demand that we ‘prepare the cabin’ (read, scare the passengers half to death!).
As expected, the landing was normal. However, what happened next was anything but normal. Let me explain a few things here. When the airplane is in the air the engines idle at a much higher speed than when the airplane is on the ground. There is a ‘ground sensing’ mechanism on the wheel struts that tells the engines the airplane is on the ground. All that is well and good, but that brings up another problem. When the airplane is on the ground and one or more throttles are pushed forward, if the wing flaps are not in the ‘take off position’ a warning horn sounds. Well, here we were, rolling down the runway, slowing down, trying to communicate with the Tower Controllers, with this warning horn sounding. Now, this horn is not a nice polite little horn like the one in your car, it is a very loud klaxon and blares constantly! There was no way we could communicate with the Tower, or with ourselves with this blasted horn blaring!
I immediately knew the problem, and I also knew the position of just about every circuit breaker in the cockpit. I quickly reached over and pulled the ‘ground sensing’ circuit breaker – instant silence, so sweet. WHOOPS, now the engines think they are in the air and go from ground idle to flight idle. The airplane went from 20 mph to 100 mph almost instantly. Well, you can’t taxi around the airport doing 100 mph, so our choices were noise, or speed. There was no other way to silence the horn, or I would have done it!
As we taxied to the gate, I would push in the circuit breaker to slow the airplane, then pull it back out to communicate. It was a bit like riding a bucking bronco, going from low to high speed; silence to blaring klaxon – instantly. And, just to add to the confusion, we were laughing so hard tears were rolling down our cheeks. It seemed a comedy of errors – no matter what we did we had one problem or the other. Once we got all our clearances, I put the circuit breaker back in so we could slow down and park. We just held our ears until we could shut down the other engines. Once they were shut down, I pulled the circuit breaker out and left it out so we could finish our work and the passengers could deplane in peace and quiet. It had certainly been an interesting half hour!
No, the rain and cold had nothing to do with our throttle problem. It turned out that somehow, the # 2 engine throttle cables had become twisted and were bound up, which is why we could not move the throttles. We were never in any real danger, but it certainly had our full attention and tested our working knowledge of the airplane systems!
By, Captain Nancy Aldrich