Published today, the following links from ATSB cover the crash of a Cessna 150 VH-RXM at Moorabbin on 18 February 2014.
Aviation Short Investigations Bulletin - Issue 31
http://www.atsb.gov.au/media/4907104...-023_final.pdf
In the days following the accident there was considerable Pprune reader comment on the circumstances surrounding the event. Accepting that the ATSB report deals with the facts I believe a valuable opportunity to educate flying school operators and their instructors was missed. As part of its reports ATSB include a motherhood statement that says: "the object of a safety investigation is to identify and reduce safety-related risk. ATSB investigations determine and
communicate the safety factors related to the transport safety matter being investigated
In this accident the inexperienced flying instructor displayed poor airmanship by permitting a TIF candidate with no flying experience to handle the controls on take off. It appears that the student was uncertain of the use of the elevator and continued to pull back on the control column which is what he thought was normal technique to climb. In the ensuing flurry of activity as the instructor tried to take control, the aircraft stalled and dropped a wing and crashed. The flying school operator changed their rules (if there were any before hand) after the event.
The following extracts from the ATSB report paint a picture leaving readers to come to their own conclusions.
The instructor noted the lowered left wing, and attempted to level the wings by neutralizing the ailerons. Almost immediately, the right wing unexpectedly dropped. The instructor realised the right wing had now stalled and applied and responded by applying left aileron to raise the right wing. By now, the aircraft nose had lowered, and a high rate of descent had developed. Realising impact was imminent, the instructor made every effort to straighten the aircraft and applied left rudder and full power in an attempt to recover.
Judging from the above sequence of events after the pitch up, it appears the inexperienced instructor used a wrong technique in his efforts to recover from a stall. He attempted to level the wings by neutralising the ailerons after the left wing dropped. If the ailerons were held neutral, it follows he must have applied opposite rudder to try to pick up the dropped wing which in turn led to the first part of an incipient spin to the right. As this accident showed, common flying school teaching that a dropped wing is picked up by neutralising the ailerons and skidding the wings level by opposite rudder, is potentially dangerous as it invites a spin. In this case his actions may have caused the right wing to drop markedly. In Cessna aircraft the ailerons are designed to be effective below the stall.
The correct method to recover from a stall with a dropped wing is to simultaneously decrease the angle of attack by forward stick, apply sufficient rudder to prevent the wing from going down further, apply full power and level the wings with ailerons. All this should take no more than 2-3 seconds if performed correctly. ATSB should have commented on the instructors incorrect recovery technique and brought the flying school training under scrutiny for allowing this incorrect stall recovery as standard operating procedure.
ATSB did say the instructor commented that RXM characteristically had a more pronounced wing drop to the right. If that was true, the aircraft was unworthy and should not have been flying. Previous flying instructors and the CFI stand condemned for not recording this defect in the maintenance release and grounding the aircraft until the defect was rectified. Part of the process of certification test flights by the manufacturer's test pilots include a tolerance of no more than 10 degrees of wing drop at point of stall. If the wing drop exceeds that, certification is delayed until the problem is rectified.
Most instructors are aware that some aircraft can exceed that tolerance during stall practice although in most cases the entry into the stall is done at a faster rate than the test pilot is required to do. Stalls in the approach configuration are also part of the certification process with a similar wing drop tolerance applied. However, there is direct evidence that flying school operators are often complacent if an aircraft is prone to a marked wing drop at the stall and even leave the defect in situ in the dangerously misplaced attitude it is handy to have an aircraft on line that drops a wing at the stall for student pilot practice. It is known as practicing bleeding. Some years ago there was one Cessna 150 in the Melbourne area that was known for its severe wing drop at point of stall. The flying school was well aware of this defect and banned student solo flying in it. When CASA airworthiness staff investigated, the aircraft owner quickly removed the aircraft from flying and re-rigged the wings which rectified the problem.
As we have seen earlier, ATSB state in their manifesto ""the object of a safety investigation is to identify and reduce safety-related risk." Well, they sure missed a golden opportunity in their accident report on VH-RXM to say something of flight safety significance about the un-airworthiness of VH-RXM and the failure of the flying school management to ground that aircraft known for its propensity to drop the right wing at point of stall. The ATSB report does not say anything about the failure of previous pilots to write up the wing drop defect in the maintenance release. It should have done so. Too many pilots are actively discouraged from writing up defects in the maintenance release for fear of job security. It takes little imagination to know what I mean. Word of mouth reporting of a defect is not sufficient.
Finally, what authority certified the grade 3 instructor as competent to instruct on stalling sequences when from the ATSB report he lacked knowledge of the correct technique. There is ample anecdotal evidence that the myth of picking up the dropped wing at point of stall with rudder only, is widely taught both on instructor courses and at flying schools in general. That being so, it suggests that CASA supervision of flying school training needs to be tightened.