I came across this report a few months ago. It has all the hall marks of any aviation accident except in this case the PIC, a flight instructor, is able to regain control and bring about a safe recovery. There is an important lesson here for light piston owners and renters. This post is based on the Transportation Safety Board report, Environment Canada weather archives, and my opinions. Let's start with the summary.
SummaryThe class 4 instructor had accumulated some 300 hours (60 hours instructional), the student 7.1 hours in nine calendar days. I can imagine them completing the ground briefing covering the lesson to be conducted, inspecting the airplane, starting and departing for the practice area. The report does not specify the weather but presumably any ceiling would have been high enough to allow the required altitude for recovery. Environment Canada archive data indicates that many of the preceding days were dominated by cloudy skies, fog and rain. The 13th is reported as mainly clear all day, certainly a good day for upper air work.
The student pilot and the flight instructor took off from the Kingston, Ontario, airport to practice stalls in the Cessna 150 aircraft. The instructor first demonstrated the stall and recovery, then had the student attempt the same procedure. On his first stall recovery attempt, the student was slow to apply back pressure on the control column to bring the nose of the aircraft up. The instructor took control with the aircraft in a nose-low attitude. When the instructor applied back pressure, he found that the elevator control was restricted from full movement. Although he exerted considerable force on the control column, he could not get the elevator control back beyond neutral.
The aircraft reached a speed of approximately 190 miles per hour before the instructor was able to slowly pull out of the dive. The instructor was able to maintain altitude and fly back to Kingston Airport for an emergency landing by using a combination of back pressure on the elevators, full nose-up trim, and an engine power setting of 2500 revolutions per minute. During final approach to the runway, as the instructor applied flap to slow the aircraft, the elevator controls became free, and he was able to carry out a normal landing. The aircraft sustained substantial damage to the wings, flaps, and ailerons as a result of the overspeed situation.
The instructor demonstrated the stall and recovery then had the student enter a stall and recovery. As the maneuver progressed the the recovery phase "the student pushed the control column forward aggressively, and the aircraft entered a dive". The instructor took over "when he judged that the student was not initiating an effective recovery." All is progressing as it should, unfortunately a very natural reaction by the student had reveled a hither to undetected flaw in the aircraft. As the instructor acted to recover from the stall he found "considerable resistance and was unable to pull the control column past the neutral position". The instructor was able to arrest the dive and maintain altitude with constant back pressure and high engine power. He set course for Kingston and declared an emergency. While maneuvering for landing he selected flaps in an attempt to reduce airspeed. In correcting for the pitch trim change caused by the flaps the instructor noticed he now had full elevator authority. A safe landing was made without further difficulty.
The aircraft was examined but no control anomalies were found. During the examination the cabin air knob was found pulled fully out. The aircraft had be retrofitted with an intercom using push to talk switches of the type that are held on the yoke with Velcro and connected to the intercom system by a self coiling cords. The cord on the right side was old and had lost much of its elasticity. The cord, now some four feet long was wrapped several times around the control yoke shaft in an attempt to keep it out of the way. It seems, however, that one of the wraps was loose enough to swing forward during the stall recovery, entangling with the cabin air knob. Once so engaged aft pressure would tighten the loop effectively jamming elevator control. In hind sight, if the instructor had released back pressure, as he did after deploying the flaps, he might have freed the controls sooner. In truth though, without identifying the fault first, he could not know if forward movements of the yoke might result in the elevator jamming in a more nose down position, resulting in a far worse situation than he was in.
In the end the only negative outcome was over speed damage to the airplane. Much less costly that it could have been. In return we get a very valuable lesson. Boxing the controls during preflight is not really enough. Are there any snares laying in wait in your airplane, or those you rent? I know I gave my airplane a close examination after reading this report.
Safe Flight.
2 comments:
That aircraft I used to complete my first solo in.
My opinion:
Factors that added to the incident was also penny pinching and not opting to buy a new cord. Something that costs under 100 dollars could have destroyed an aircraft and two people. It is a hidden risk, but it stems from an attitude I believe of literally "stretching" the life out of equipment and saving money at a cost to safety.
Once the radio was u/s and a hand held was placed in the aircraft as the sole radio. That's fine if it's just me flying my own aircraft but not if I was running a flying school.
Again my opinion...
Also I wondered who the hell would try and operate the flaps after doing almost 200 mph in a 150 ? After that so much as a mouse fart would rid you of the wings :)
Safe flying !
Small world. I will admit to inferring that the root cause was aggressive economizing, I even toyed with some text to that effect, but finally decided the subtext was obvious. I'm glad to have firsthand confirmation though.
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