1991 Merion mid-air collision

Investigation

A National Transportation Safety Board (NTSB) investigation was opened almost immediately. Investigators cited a litany of mistakes and wrong decisions that led to the deaths and injuries. "This was a senseless accident that didn't have to happen," said James L. Kolstad, then-chairman of the NTSB.

In September 1991, the NTSB's finding were announced. It was determined that the poor judgment of both flight crews caused the accident.

The NTSB report stated that visual checks from the helicopter and control tower were pointless because the nose gear doors of the Aerostar partially close when the gear extends, obscuring most of the locking mechanism and making it "virtually impossible" to determine even from an "unsafe distance" whether the nose gear was locked. No useful information could have been provided beyond what the pilots had already determined for themselves by looking at the propeller spinner reflections, the NTSB said, noting that the Aerostar pilots should have realized this due to their presumed familiarity with their own aircraft. The NTSB said that the helicopter crew should have also realized the futility of the task due to the inherent difficulty of seeing fine detail while looking upwards through the Bell's front windshields. The Bell was equipped with overhead windows, but the operator had painted them over because light flicker from the main rotor had caused pilots to experience vertigo.

The NTSB criticized the Piper flight manual for lacking explicit procedures to follow if the nose gear indicator light would not illuminate. However, the aircraft was also equipped with a landing gear warning horn that would sound if the throttles were moved to the idle position when the gear was not down and locked; the pilots could have verified whether the gear was locked by reducing throttle at a safe altitude and listening for the horn, which was part of the procedure in the flight manual if the landing gear hydraulics failed. The NTSB could not determine whether this was attempted, as the Aerostar was not equipped with a cockpit voice recorder, but the NTSB concluded from radio communications with controllers that the pilots most likely did not attempt it. Even if the procedure was fruitless, the NTSB said that with the nose gear visibly in the down position, a more experienced pilot probably would have still attempted a landing "accepting the possibility that the nose gear could collapse during the landing roll", as such a condition "does not generally result in a major accident or occupant injury".

The NTSB noted that none of the pilots had any formal experience or training in formation flying; the helicopter pilots had flown close to another helicopter in the past, but at a considerably greater distance than in the accident flight, and it was not known if they had ever flown near a fixed-wing airplane. The NTSB said that aerodynamic forces tend to pull aircraft toward one another when one flies immediately above another, and assertive flight control corrections may be required to counteract this; although radar data was inadequate to determine if such an event had in fact occurred, Bell Helicopter engineers confirmed that the 412SP is subject to this tendency. The NTSB faulted the crews of both aircraft for attempting unfamiliar and inherently risky maneuvers over a populated area, as both aircraft had ample fuel, and there was no other factor present that would compel the pilots to finish the inspection quickly. The NTSB recommended that the Federal Aviation Administration (FAA) make a more concerted effort to train pilots to recognize such hazardous situations and exercise better judgment.

Due to collision, ground impact, and fire damage, the NTSB was unable to determine if the Aerostar's nose gear or the nose gear warning systems were functioning properly before the crash.