Could a rigging error, causing different angles of incidence from one wing to the other, have caused or exacerbated the vicious stall characteristics?
I once flew a Ceesna 152 from a flying school. At the time I was an instructor giving another instructor recurrent training as he had not flown for several months. I asked him to demonstrate a clean stall and recovery. He entered the stall smoothly and we were both taken completely by surprise when the aircraft dropped the left wing viciously to 60 degrees with the nose dropping to 30 degrees nose down. We lost 400 feet in the recovery. I had flown old military aircraft some with wing drop characteristics and was very experienced. But even then that Cessna 152 was one of the worst wing drop examples I had flown.
I took control and set up for another stall with full flap and 1500 RPM. Again,an equally sudden wing drop at the point of stall and by the time we recovered we had lost 600 ft and finished up 180 degrees from the original heading. There was no doubt the aircraft was un-airworthy and I reported the problem to the flying school as well as writing the defect in the aircraft maintenance document. The CFI stated he knew about the wing drop problem on that particular aircraft but was happy to accept the defect because he used it for PPL tests to test the students competency at recovering from a wing drop; this being a regulatory requirement for the PPL test.
Solo flying was not permitted by the flying school on that Cessna 152 because of the wing drop risk. The owner of the aircraft was a licenced aircraft mechanic who did his own maintenance. After I had recorded the wing drop defect in the maintenance document the owner signed off the aircraft as serviceable without rectification and it continued to be hired out.
Eventually action was taken by one disgruntled hirer to contact the Regulator as he was concerned the aircraft was being flown despite being demonstrably un-airworthy even though the maintenance document displayed a clean sheet devoid of defects. The Regulator sent an Examiner to test fly the aircraft. When the mechanic owner of the Cessna 152 realised a CAA Examiner had booked the aircraft for a test flight, he took the aircraft off line and re-rigged the wings before handing it over to the Examiner to test fly. The owner failed to tell the Examiner that he found the left wing to be grossly out of correct rigging and that he had now rectified the defect. The Examiner flew the aircraft testing the stall characteristics which by now were normal following the rectification by the owner. He reported to the Regulator that the Cessna 152 had no defects
Later, the disgruntled hirer who had experienced the severe wing drop was admonished by the Regulator and informed an Examiner would test him for his knowledge of recovery from a wing drop at the point of stall. The disgruntled hirer happened to be another experienced miliary pilot with thousands of flying hours and thus familiar with wing drop characteristics.
That Cessna 152 had been flown by many flying school instructors in the months before the first episode. While they were aware of its adverse stall characteristics through word of mouth, none would record the defect in the maintenance record for fear of job security. This is a common problem in general aviation operations. If any aircraft flown by students and instructors is found to have undesirable handling characteristics during stalling practice it becomes a flight safety issue. It becomes an airworthiness issue as well. Unless the pilot records the defect on the maintenance document as well as verbally to the operator, the next pilot to fly the aircraft could be in for an unpleasant surprise. There is also a moral obligation to report these sort of defects.