On April 4, 1991, a Lycoming Air Services Piper Aerostar, PA-60, N36450, was operating as an on-demand air taxi flight under 14 Code of Federal Regulations (CFR) Part 135. The airplane departed the Williamsport-Lycoming County Airport (IPT), Williamsport, Pennsylvania, around 1022 eastern standard time on an instrument flight rules (IFR) flight plan for the Philadelphia International Airport (PHL), Philadelphia, Pennsylvania. The captain, first officer, and one passenger were on board.
The takeoff and en route portions of the flight were uneventful. As it approached PHL, the flight was cleared for an instrument landing system approach to runway 17. While on the approach at120 l: 28, the captain of N36450 reported that the nose landing gear position light had not illuminated to indicate that that the nose landing gear was in the down and locked position and that he might need to cycle the landing gear. Lycoming Air Service representatives, upon listening to air traffic control (ATC) recording, identified the captain's voice as making the transmissions from the airplane. Lycoming Air Service officials reported that the PA-60 is normally a single-pilot airplane. The Safety Board believes that the captain was flying the airplane, as well as making the radio transmissions.
Shortly before N36450 be91an its approach, a Bell 412SP helicopter, N78S, operated by Sun Company Aviation Department, departed from the company's helicopter landing pad at PHL on a visual flight rules (VFR) flight to Sun Company corporate headquarters in Radnor, Pennsylvania. The captain and first officer were the only persons on board. The aircraft was operated under 14 CFR Part 91. As N78S departed the PHL terminal control area (TCA), the pilots heard the communications regarding the possible unsafe nose gear indication on N3645D.
The crew of N36450 was told to maintain l,500 feet to allow N78S to pass underneath as the helicopter departed the area. As he passed under N3645D, at 1202:29, one of the pilots of N78S reported to the tower “that Aerostar that went past us, looks like the gear is down." Sun Company personnel identified the voice making the radio transmissions from the flight to ATC as being that of the first officer. However, several subsequent transmissions from N78S were made by the captain. The chief pilot for Sun Company indicated that the flight crew wore headsets equipped with boom microphones and that there were push-to-talk buttons on the flight controls. Thus, it would not be unusual for the flying pilot to transmit. The Safety Board believes that the captain was flying the helicopter, but the pilots may have switched flying roles at times during the flight.
The captain of N364SD acknowledged to ATC that he had heard N78S' s transmission and stated that "I can tell it's down, but I don't know if it's locked, that's the only problem." A reflection of the nose landing gear can be seen from the cockpit on the propeller spinner. The tower acknowledged the transmission and advised that the helicopter was no longer a factor and that N36450 was cleared to land on runway 17. The controller later stated that he interpreted N36450's situation as justifying an emergency. The tower supervisor alerted the airport's aircraft rescue and firefighting units (ARFF). Additionally, runway 17 arrivals were terminated through a coordinated effort between the tower and approach control , resulting in a relatively clear communications frequency. The local controller contacted N3645D and requested the number of occupants and amount of fuel on board.
At 1203:35, the controller offered N16450 the option of making a low altitude pass by the control tower so that the tower personnel could observe the position of the nose gear. The controller further stated that there was "almost no traffic right now - we can do whatever you like." N3645D acknowledged that it would do a flyby of the tower. At 1.204:12, the captain of N78S advised the tower that they "could take a real close look at that if you wanted. The tower acknowledged the transmission. At 1204:19, the captain replied that N78S was turning back to the airport, presumably to perform an in-flight inspection of N36450's nose gear.
As N36450 passed by the control tower, the controller advised that the nose gear appeared to be down. The captain of N36450 responded that he could see the nose gear in the reflection of the propeller spinner and that it appeared to be do\tin, but the indicator light was not green. The controller requested N3645 to make a left turn and enter a downward leg for runway 17. He further advised that N7AS was inbound from the north and that N78S could take a look at the nose gear. At 1205:30, the captain of N36450 stated "Okay, I appreciate it." The controller further advised that the ARFF equipment was on the runway.
Sun Company officials reported that it was company policy to be "good neighbors" and that they had offered the services of the company’s aircraft and flight crews to local communities in the event of emergency situation, such as medical evacuations, and searching for lost persons. Several controllers reported that the Sun helicopter had, on previous occasions, assisted the tower in locating vehicles or people on the airport property. The chief pilot for Sun Company stated that he was not aware of any previous in-flight inspections of other aircraft by the pilots of N78S or other Sun Company pilots.
Commencing at 1205:45, the controller provided directional information to the flight crew of N78S to assist in visually acquiring N365D. This information was acknowledged by the first offic1 r. By 1207:54, the pilots of each aircraft acknowledged that they had each other in sight and that a speed of 125 knots would be used during the join up. At that time, the aircraft were joining up on an extended downwind leg for runway 17 at an altitude of about l, 100 feet. The controller advised N36450 of antenna towers 6 miles ahead and requested the pilot of N36450 to notify the tower when he wanted to turn back toward the airport or make a heading change.
At 1208:21, the captain of N78S contacted N3645D directly on tower frequency and requested that the pilot of N3645 slow down. At 1208:52, the first officer of N78S contacted N3645D and stated that "we're going to come up behind you on your left side so just ho1d your heading." The captain of N36450 responded that the antenna towers were straight ahead and that he might need to change heading by 115 degrees to the left. At 1209: 30, the first officer of N78S stated on tower frequency "Aerostar, we're gonna pass around your right side now, take a look at everything as we go by." The captain of N3645D responded with "Okay." At 1210:00, there was a transmission from N3645D that was unintelligible because of a transmission from another aircraft. The controller asked N3645D to repeat the transmission, and the pilot of N36450 again stated that the indicator for the nose gear did not show down and locked.
At 1210:16, the first officer of N78S stated "everything looks good from here. The captain of N3645D replied "Okay, appreciate that we'll start to turn in." These transmissions were the last ones received from either N76S or N36450. The last transmissions was abruptly terminated by considerable noise. At 1210:51, the controller requested N36450 to make a left turn back to the airport, and he cleared the airplane to land on runway 17. Short1y thereafter, the controller noticed a smoke p1ume to the north of the airport. Subsequent attempts by the controller to contact either the N78S or N3645D by radio were unsuccessful.
The witnesses reported that after the collision they saw fire on the right side of the airplane and fire on top of the helicopter's cabin. Witnesses reported that numerous parts came off both aircraft following the collision. The investigation determined that the outer right wing panel from N3546D and one of the main rotor blades from N78S had separated from the respective aircraft as a result of the collision. Therefore, both aircraft were rendered uncontrollable because of damage from impact with each other.
N3645D came to rest in the front yard of the Merion Elementary School just to the right of the entrance loop to the school. N78S came to rest just behind the school building. The flight crews aboard both aircraft and the passenger aboard N36450 were fatally injured. Two persons on the ground at the rear of the school were fatally injured by debris. One person on the ground was severely injured by fire. Four other persons received minor injuries.
Th, accident occurred about 1210:20, during the hours of daylight, at 40° 00' 05" north latitude and 75° 15' 26" west longitude. At the time of the collision, both aircraft were outside the TCA for PHL.
Both aircraft were destroyed by impact with the ground and post crash fire. The value of the Piper PA-60 was estimated at $135,000 before the accident. The value of the Bell 412 helicopter was estimated at $4,500,000 before the accident. Several private residences were damaged by falling debris. In the school yard, one tree, landscaping timbers, and lawn grass were destroyed or substantially damaged by impact and the post crash fire.
We determined that the probable causes of this accident were the poor judgement 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 eextended, the poor judgement of the captain of the helicopter to conduct the inspection, and the failure of the flightcrew of the helicopter to maintain safe separation. Contributing to the accudent was the incomplete training and checking that the flightcrew of N3645D received from Lycoming Air Services, Inc., and the FAA principal operations inspector assigned to the operator.
As a result of the investigation, we issued recommendations to the Federal Aviation Administration, the National Business Aircraft Association, the Helicopter Asscoiation International, and the Aircraft Owers and Pilots Association.
