Aviation Safety Letter 2/2003
To The Letter
Lowering flaps after overspeed...
I was somewhat concerned after reading the article Wrapped Radio Cord Causes Control Problems in ASL 2/2002. In particular the line "During a long final approach, the instructor lowered the flaps in an attempt to slow the aircraft to a lower touchdown speed." This is an aircraft that had just been subjected to a serious overspeed condition. As was noted later on in the article, the flaps had been "extensively damaged." C150/172 aircraft have had a number of flap asymmetry incidents due to damaged flap tracks and an overspeed is an excellent way to do exactly this sort of damage. Lowering potentially damaged flaps is, in my opinion, asking for problems. There is a risk of a one flap lowering further than the other resulting in an uncontrollable roll. Additionally, there is a good chance of the damaged flaps jamming in position such that retraction might not be possible even if the pilot had time to react given the low altitude (on final) at which flaps were selected. Unfortunately, the Cessna 150 manual gives very little guidance on emergency procedures following an overspeed and as pilots we have little "official information" to go on in an emergency such as this. While this aircraft landed safely, it should be stressed that the procedure of lowering flaps (or making any configuration change) after a severe overspeed is not advisable unless it is absolutely critical to landing the aircraft.
Phil Laird, P.Eng., Ste-Foy, Quebec
Brakes freeze while sitting in slush
The lead article "Just a Bit of Slush" by William Ives, as published in ASL 1/2003, is excellent and most informative. I can, however, add an additional "winter flying note" based on an experience I once encountered. The outside temperature was below freezing when I was cleared to taxi to Runway 24R at Toronto's Lester B. Pearson International Airport; the taxiway was quite slushy and the wind was quite strong at the time. I was flying a Bellanca Crusair "tail-dragger" and as it did not have a steerable tail wheel, considerable use of brakes was necessary to keep the aircraft proceeding in a straight line to the take-off holding position where I had to wait for several minutes for aircraft ahead of me to depart. Thus, it was quite an embarrassing moment for me when the tower finally cleared me to the runway to line up and hold, as even with full throttle the aircraft would not budge. This dilemma was caused by slush and snow on the taxiway being thrown against the heated brake drums on the wheels. During the 10-minute wait for take-off clearance, with the help of the wind and below-freezing temperatures, the liquid that impregnated the wheels and brakes froze solidly and prevented the wheels from turning. Luckily my passenger was another licensed pilot who was able to break the ice free at the wheels so we could continue our journey. Lesson learned — plan to keep those wheels constantly turning under such circumstances to prevent the brakes from freezing.
Bill Peppler, Ottawa, Ontario
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