FLIGHT CONTROLS: FREE AND CORRECT ….
Acknowledgements: “THIS AVIATION LIFE” (George Scheer - www.thisaviationlife.com)
“Ever wonder why your before-flight checklist reads “Flight Controls: Free and Correct?” (If it doesn’t, it should.) Ever watch another pilot run through that particular safety check by simply “boxing the controls?” Not so long ago, one of the most careful pilots I have ever known, and one of the most diligent, might well have lost control of the airplane he has spent fourteen years building with the most exquisite attention to detail.
Retrieving his airplane after weeks in the paint shop applying a stunning custom paint scheme, the electric pitch trim operated in reverse when he tested it before take-off. A less careful pilot might well have launched without checking the operation of the trim and become confounded immediately after take-off by the paradoxical effect, responded in panic, and lost control of the airplane.
As the builder, and therefore qualified to maintain and repair his airplane, he had re-installed the controls after they were painted and had reversed the mechanical linkages to the trim actuator. Fortunately, he understood the meaning of “free and correct” and had discovered the reversal before take-off.
(However), in the summer of 2014, in Anchorage, Alaska, the pilot of a Piper PA-12 Super Cruiser had failed to make the same check, and it cost him his life. The National Transportation Safety Board report on the fatal accident concluded that mis-rigging of the elevator control cables, such that a forward movement of the stick resulted in an upward deflection of the elevator, was the proximate cause of the accident - and that a proper before take-off check of control movement being free and unrestricted and in the correct direction would have alerted the pilot to the error. Observers of the take-off from Merrill Field in Anchorage reported that after take-off the Piper pitched up at an alarming angle, climbed vertically, then pivoted and descended in a near-vertical path to the ground, behaviour consistent with a departure stall.
The PA-12 had been extensively modified and refurbished over several years, with much of the work apparently done by the owner and pilot and with very little of the recent work properly noted in the maintenance logs. The maintenance was poorly documented but the pilot’s acquaintances supported his ability and diligence, and remarked that the work had been carried out under the supervision of an A&P with Inspection Authority.
As a result of this accident and others, the NTSB issued Safety Alert SA-041 cautioning pilots and mechanics to be aware of the possibility of mis-rigging an airplane after maintenance.”
“SA-041 -Pilots: Perform Advanced Pre-flight After Maintenance
BE VIGILANT FOR FLIGHT CONTROL AND TRIM ANOMALIES
· In-flight emergencies, accidents, and deaths have occurred after pilots flew aircraft with incorrectly rigged flight control or trim systems.
· Four such mishaps within a 2-year span share common safety issues:
- Maintenance personnel who serviced or checked the systems did not recognize that the control or trim surfaces were moving in the wrong direction.
- Pilots who flew the airplanes did not detect the control anomalies during their pre-flight checks.
In many cases, although maintenance personnel made mistakes, the pilots could have prevented the accidents by performing thorough or advanced pre-flight checks.
What can pilots do?
· Become familiar with the normal directional movement of the flight controls and trim surfaces of the aircraft you fly before it undergoes maintenance. It is easier to recognize “abnormal” if you are already very familiar with what “normal” looks like.
· After maintenance, check systems more thoroughly than the normal pre-flight checklist implies. For example, if a pre-flight checklist states, “Trim – Set Take-off,” verify not only the trim setting but also proper directional travel (Watch the control surfaces as you check).
· Be prepared to abort the take-off if something does not seem right.
· Avoid interruptions and distractions during your pre-flight inspection to ensure that you do not skip or misevaluate the items you are checking.
· If you suspect that there is a problem with a flight control or trim system, ask qualified maintenance personnel to inspect the aircraft. Do not attempt to perform such work yourself if you are not appropriately qualified, certificated, and authorised to do so”.