Investigation Summary
The accident sequence began when the crew of the Piper Aerostar noticed the nose gear 'locked' indicator light failed to illuminate during approach to Philadelphia. Despite seeing the gear reflected in the propeller spinners and receiving confirmation from the control tower that the gear appeared down, the pilots remained uncertain if it was locked. A Sun Company Bell 412SP helicopter in the vicinity offered to perform a close-range visual inspection. Neither crew had formal training in formation flying. As the helicopter moved underneath the Aerostar to inspect the gear, the two aircraft collided. The helicopter's rotor blades struck the Aerostar's left wing, leading to the immediate structural failure of both aircraft. The NTSB highlighted that the inspection was fundamentally flawed because the Aerostar's gear doors partially obscure the locking mechanism when extended, making a visual confirmation of a 'locked' status impossible from another aircraft. Furthermore, the helicopter pilots' visibility was hampered because their overhead windows had been painted over to prevent rotor flicker vertigo. A key NTSB finding noted that aerodynamic forces tend to pull aircraft toward one another when one flies immediately above another, a phenomenon known as aerodynamic interference or vortex effects, which likely contributed to the collision as the helicopter maneuvered in close proximity.
Final Conclusions
The National Transportation Safety Board determined the probable cause was the poor judgment of the flight crews of both the Aerostar and the helicopter, who initiated an unbriefed, lead-and-follow formation flight without adequate training or a clear operational necessity. Contributing to the accident was the lack of specific procedures in the Aerostar flight manual for troubleshooting a landing gear indicator failure and the decision to conduct the maneuver over a densely populated area.
Video Analysis
When Being a 'Good Neighbour' Turns into TRAGEDY — A detailed look at the 1991 Merion air disaster involving Senator John Heinz, exploring the series of pilot errors and the tragic impact on a local elementary school.
If playback is blocked, the owner has disabled embedding — use the link above.
Crew Experience
Captain
The pilot had significant total experience but relatively low time on the Aerostar type.
Captain
First Officer
Systems & Failure Modes
Landing Gear Indicator
A green light in the cockpit that signals the landing gear is down and mechanically locked; its failure to illuminate triggered the troubleshooting sequence.
Landing Gear Warning Horn
A backup system designed to sound if throttles are retarded to idle while the gear is not locked; the NTSB noted pilots could have used this to verify gear status.
Interesting Facts
- 01All five occupants of the two aircraft and two children on the ground were killed.
- 02The Aerostar was not equipped with a Cockpit Voice Recorder (CVR).
- 03The helicopter's overhead windows were painted over to prevent pilot vertigo from rotor flicker.
- 04The NTSB concluded the visual inspection was futile as the gear locking mechanism is obscured by doors when extended.
- 05Senator John Heinz was the sole passenger on the Piper Aerostar.
Safety Actions & Advisories
Aeronautical Decision Making (ADM) Training
The NTSB recommended the FAA emphasize ADM and the recognition of hazardous situations, specifically regarding the risks of impromptu formation flying.
Flight Manual Revisions
The NTSB criticized the lack of explicit troubleshooting steps for gear indicator failures in the Piper Aerostar manual, leading to calls for clearer emergency checklists.