By the Book

A midair over Philadelphia

January 1, 1992

Few aeronautical activities are riskier than formation flying when the pilots involved are not trained, experienced, practiced, and proficient in the special skills required to perform such a maneuver. And the risk is entirely avoidable because there is virtually no situation in civil aviation in which formation flight is required. When it is practiced, it is essential that the flight — including emergency procedures — has been meticulously planned in advance, and that the plan is adhered to.

None of these conditions prevailed when a Piper Aerostar and a Bell 412SP helicopter collided in flight near Philadelphia last April. The two aircraft crashed into a schoolyard. The four pilots and the passenger on board the Aerostar, Senator John Heinz, were killed. On the ground, two children were killed by falling debris, another person was severely burned, and four people received minor injuries.

The Aerostar had been on approach to Philadelphia International Airport. When the pilot extended the landing gear, the nose-gear-down indicating light failed to illuminate. The pilot could see from the reflection of the nose gear in the propeller spinners, however, that the gear appeared to be fully extended. This was confirmed by the crew of the helicopter, over which the Aerostar passed on its approach, and again by controllers during a flyby of the control tower.

With an Aerostar's gear doors closed over the wheel well area, the nosegear locking mechanism is concealed. Hence, there was no additional information to be gained by the flyby or by an in-flight inspection from another aircraft. Yet when the 412 crew (one of whom had experience in Aerostars) offered to take "a real close look," the Aerostar pilot acquiesced.

The tower controller provided directional information to assist the 412 crew in visually reacquiring the Aerostar. The 412 crew maneuvered toward the Piper, and the first officer transmitted, "Aerostar, we're gonna pass around your right side now and take a look at everything as we go by." Forty-five seconds later, he reported, "Everything looks good from here," and the Aerostar pilot responded, "Okay, appreciate that, we'll start to turn in." This last transmission was "abruptly terminated by considerable noise," according to the National Transportation Safety Board accident report.

The accounts of witnesses regarding the movements of the aircraft at this point differed considerably, and we'll probably never know the exact sequence of events. What became clear during the investigation, however, is that the leading edge of one of the helicopter's main rotor blades came in contact with the Aerostar's right main landing gear tire, while the tip came in contact with the nosewheel tire. That blade separated from the hub, and the outer right wing panel separated from the Aerostar, rendering both aircraft uncontrollable.

The reader can appreciate the motives of the 412 crew in seeking to assist a fellow pilot. Indeed, the helicopter's operator had an official policy of offering the services of the company's aircraft and flight crews to local communities for emergency services such as medical evacuations and searches for lost persons. The company's chief pilot was unaware, however, of any case in which his flight crews had engaged in an in-flight inspection of another aircraft. He had once told the two pilots involved in this accident that if they ever were involved in in-flight observation of another aircraft, they should maintain at least 300 to 700 feet of separation.

The sad facts are that none of the four pilots involved had any experience in flying in close proximity to another aircraft; that the Aerostar pilot did not coordinate with the 412 crew on the maneuvering procedures to be used; that the 412 crew maneuvered into a position from which the helicopter could not be seen from the Aerostar's cockpit; that the 412 crew failed in their responsibility to maintain safe separation; and that the operation was undertaken over a densely populated area.

There is no evidence that the pilots were aware of the potentially hazardous aerodynamic interactions this flight regime offered. For one thing, turbulence-induced blade stall and settling may be experienced by a helicopter flying below and behind a fixed-wing aircraft. In addition, as noted in the NTSB report, "the textbook Aerodynamics for Naval Aviators specifically refers to the case of one aircraft inspecting the landing gear of another. It states that when one aircraft is flying closely behind and below another, the lower aircraft experiences a nose-up pitching moment and the higher aircraft experiences a nose-down pitching moment.... [T]he opposing pitch moment changes can be large and must be anticipated or a collision may result. Engineers at Bell Helicopters have stated that the Bell 412 would experience such a nose-up pitch change." indeed, the final seconds of raw radar data suggest an upward movement of the helicopter toward the Aerostar may have occurred.

Because no cockpit voice recorder was installed in the Aerostar (nor was one required), we have no idea of what troubleshooting the pilot may have done to ascertain the status of his gear beyond what he could see reflected in his spinners. We know that, on the oral portion of a flight check a little over a week before the accident, the pilot satisfactorily responded to questions on emergency gear extension procedures. We also know that a training/check pilot told the NTSB he had instructed the pilot regarding the push-to-test function of the gear indicator lights. But we do not know if the pilot was aware that he could test the nose-gear downlock by retarding the throttles — a horn would have alerted him if the gear was not locked in place. The training/check pilot stated that he had not instructed the pilot on the operation of the landing gear warning horn, and the NTSB found that the emergency procedures section of the Aerostar flight manual does not contain sufficient information on the actions to take if the nose-gear light fails to illuminate.

Chances are a landing could have been successfully accomplished with little or no damage to the airplane and no injury to its occupants. Poor decisions on the parts of both of the flight crews led to an entirely different outcome.

The NTSB determined "that the probable causes of the accident were the poor judgment by the captain of the airplane to permit the in-flight inspection after he had determined to the best of his ability that the nose landing gear was fully extended, the poor judgment of the captain of the helicopter to conduct the inspection, and the failure of the flightcrew of the helicopter to maintain safe separation."

There is little or nothing to be gained by an in-flight inspection or other close-proximity maneuvering in general aviation aircraft. To do so without proper training and strict adherence to safe operating practices is to court disaster.

The NTSB is solely responsible for determining the probable causes of accidents. Information contained in this "By the Book" is derived from the NTSB aircraft accident/incident summary report.