Asymmetric Accidents

• There were 477 light twin accidents following engine failures during the period under review. One hundred and twenty-three of these were fatal smashes in which 289 people died.

• Accidents following engine failures of these types generally involve a lack of proficiency in responding to these emergencies. Often these accidents involved some degree of panic, probably related to inadequate immediate recall of the exact emergency procedures – or lack of confidence in one’s ability to execute the emergency procedures.

These symptoms, according to the Board’s investigators, are indicative of insufficient recurrent training in engine failure emergencies.

• The accident rate in light twins is much lower in the category involving pro flying than for the category involving primarily non-professional flying, adds the report.

Stalls, collisions with the ground/water and collisions with obstacles accounted for 92 per cent of the fatal following engine failures.

Manuals came in for their share of criticism in the Board’s report; some handbooks lacked accelerate-stop distances or information on single-engine climb performances over obstacles. Others showed take-off and landing speeds below Vmc, and no warning was given to the pilot regarding the fact.

Climb performance was often given for zero yaw or near-zero yaw conditions, following an engine loss on take-off.

This lower drag configuration generally requires up to five degrees of bank into the ‘live’ engine.

Despite the fact that reducing yaw in critical situations might mean the difference between establishing climb or being unable to hold altitude, the pilot in many cases was not given this critical information.

A number of typical cases are cited in the NTSB Special Study:

• The pilot of a PA-23-160 crashed after losing power on the left engine shortly after take-off. He rotated at or below Vmc, and when one engine lost power didn’t land back on the 4000ft of available runway. He also apparently failed to identify and execute the proper responses.

• A Beech 58 pilot lost power on his left engine on take-off. He crashed from 150ft. Verdict: caught by surprise, the pilot lost valuable time deciding what action to take first, allowed his flying speed to erode through inattention and spun in.

• A Cessna 421 lost port engine power soon after take-off. The pilot later admitted he had panicked, uncertain of the proper emergency procedures and his ability to carry them out. He had also let his aircraft slow to below Vmc twice during the emergency.

• A Cessna 421A was being flown by a company executive, with a company pilot in the other front seat. The left engine power was lost just after the gear came up. The crash indicated a lack of understanding of aircraft performance and emergency procedures during single-engine flight, plus the executive’s reluctance to do anything but rely on the other pilot.

• The pilot of a PA-23-250 lost power on the right engine soon after take-off and, according to radio broadcasts, had sounded panicky until he crashed. Friends of the pilot later said he was “afraid” of the aircraft.

There were common factors in these and other accidents listed:

• The presence of stress disrupted the pilot’s ability to recall producers and make proper selections, and interfered with the motor responses essential for effective control of the aircraft.

• Lack of knowledge of single-engine performance of the aircraft.

• Lack of understanding of the proper single-engine emergency procedures.

• Lack of proficiency in executing the proper emergency procedures.

A series of interviews was conducted among multiple pilots with experience ranging from 20 to 8000 hours produced some eye-opening responses.

One question was simple, “Do all light twins have a single-engine climb capability?” About 25 per cent of the pilots said yes, 65 per cent said no, and the rest didn’t know.

Another question concerned the certification and performance of light twins; it was, “Is Vmc a constant or a variable?” Some of the answers include; Vmc is constant. Vmc varies. Vmc could be lower but not greater than the Manual figure. And Vmc could not be less than the Manual figure.

Among recommendations, the Special Study hints that multi-pilots undergo a complete flight review in a multi-engine aircraft within the previous 24 months, before he or she is allowed to act as pilot in command – and a special power-loss test be given during that check.

The tables in the volume make an interesting study. They show that engine failure accident rates go up with higher power loadings.

It would be interesting – and welcome – to see studies such as the NTSB one published by the Australian Department of Transport, giving vital insight and some sort of datum point from which to start a significant drive against this type of accident, using knowledge as the weapon.