1968 — Dec 24, Allegheny Air 736 night approach crash in snowstorm, Bradford, PA — 20

–20 Aviation Safety Network. Accident Description. Allegheny Air Flight 736, 24 Dec 1968.
–20 Kimura. World Commercial Aircraft Accidents 3rd Ed., 1946-1993, V.1. 4-11-1994, p. 3-11.
–20 NTSB AAR. Allegheny Airlines… Near the Bradford Regional Airport, Dec 24, 1968.

Narrative Information

NTSB Synopsis: “On December 24, 1968, Allegheny Airlines Flight 736, a Convair 580, N5802, crashed. at approximately 2012 e.s.t., while executing an instrument approach to Runway 32 at the Bedford Regional Airport, Bradford, Pennsylvania. There were 20 fatalities among the 47 persons on board the aircraft.

“The aircraft made initial contact with trees approximately 2.5 nautical miles from the end of Runway 32 at an altitude of 2,081 feet m.s.l…. The aircraft thereafter struck a tree at 33 feet above ground level and rolled to an inverted position before striking the ground.

“The weather observation in effect for Bradford Airport at the time of the accident shoved an estimated ceiling 2,000 feet broken and visibility of 1 mile in very light snow showers and blowing snow. An observation recorded 2 minutes after the accident showed in indefinite ceiling 800 feet obscuration and visibility 1 mile variable in light snow showers and blowing snow, with visibility variable between 1/2 and 1-1/2 miles.

“The Board determines that the probable cause of this accident was the continuation of the descent from the final approach fix through the Minimum Descent Altitude and into obstructing terrain at a time when both flight crewmembers were looking outside the aircraft in an attempt to establish visual reference to the ground. Contributing factors were the minimal visual references available at night on the approaches to the Bradford Regional Airport; a small but critical navigational error during the later stages of the approach; and a rapid change in visibility conditions that was not known to the crew.”

History of the Flight

“Allegheny Airlines Flight 736 (AL 736) of December 24, 1968, was a regularly scheduled passenger flight originating in Detroit, Michigan, and destined for Washington, D. C., with en route stops at Erie, Bradford, and Harrisburg, Pennsylvania. The aircraft utilized was a Convair 580, N5802….

“At 2006:25 AL 736 reported over the VOR outbound at the beginning of the instrument approach procedure. At that time Erie Approach Control instructed the flight to contact Bradford Flight Service Station (FSS)….

“Almost all of the survivors of AL 736 recalled that the stewardess had announced that the flight was approaching Bradford Airport and that the passengers should observe the “Seatbelt” and “No Smoking” signs. The survivors generally described the descent as smooth and normal, with no forewarning of the impending impact. Most of them either were dozing or had their attention focused outside the cabin.

“Most of the passengers who were looking outside the aircraft observed moderate to heavy snow….

“Several survivors stated that the first sign that anything was wrong was the sound of tree branches scraping against the aircraft, while others described the first contact as a “bump” or a hard landing. A number of survivors also observed flashes of light both inside and outside the aircraft.

“Of three survivors seated in the right rear of the passenger compartment, one stated that ‘at impact the wings tore off,’ another saw ‘the wing and the engine go by,’ while the third stated that ‘the right engine burst into flames.’ A number of survivors reported that the aircraft appeared to bounce into the air, after which it rolled or turned over to the right, and then slid to a stop in an inverted position….

“There was no evidence of sustained burning of fuel tanks or associated structure, or that any part of the main wreckage continued to burn after coming to rest. Nor was there any indication of pre-impact fire.

Survival Aspects

“The aircraft came to rest in an inverted position with the top portion of the fuselage structure torn away. More specifically, the damage to the upper fuselage began just below the windshield and extended aft in a diagonal plane to the top of the fuselage at the rear cabin door.

“Twenty-six of the 27 survivors were seated in the rearmost nine rows of seats (out of a total of 13 rows). The remaining survivor was located in the front row left aisle seat.

“Most of the survivors who remained conscious recalled that when the aircraft came to rest, they were still in their seats with their seatbelts fastened. One stated that he was separated from his seat…and ended up on his back, across the aisle, with his seatbelt hanging around his waist. A number of passengers related that they came to rest with their head or face pressed into or against the snow and dirt.

“Many of the survivors were able to unbuckle their seatbelts and fall or ease themselves down onto the ceiling of the inverted aircraft. These persons then began to search for exits from the plane and to help others out of their seats. The primary means of exit utilized were the rear left cabin door, which apparently was torn off at impact, and a hole in the left side of the aircraft near the wing.

“Those who were able to exit the aircraft without assistance went back inside and helped evacuate everyone they could. During this period, some of the survivors started a fire at some distance from the aircraft using wood, seat cushion material, and small pieces of baggage. As the survivors were removed from the aircraft, they grouped around the fire to wait for help. It was extremely cold and windy, and moderate to heavy snow was falling.

“Several of the survivors recalled observing aircraft overhead while waiting at the fire. After what one survivor estimated to be an hour, rescue personnel arrived and proceeded to extricate the surviving passengers still pinned in the wreckage. The injured survivors who were unable to walk out with or without assistance were evacuated by various means, including stretchers, jeeps and snowmobiles….

Analysis

“Based on information, derived from the flight data recorder, the flightpath flown by AL 736 during its approach t o the Bradford Regional Airport was consistent with the prescribed procedures with the exception of there being no level-off at the MDA [Minimum Descent Altitude]. The execution of the approach was flawless up to, and beyond, the 2.9 mile DME fix and until approximately 17 seconds prior to impact. At that time, the aircraft passed through the MDA in a steady descent of approximately l,500 feet per minute, which continued without change until contact with the trees occurred. There is no evidence that the crew became aware of the proximity of the aircraft to the ground until initially striking the trees, after which the first officer cried “pull up.“ It then appears that the crew made an attempt to arrest the descent but there was insufficient time t o do so since approximately 1 second later, the right wing struck a large tree, resulting in an asymmetrical lift condition which caused the aircraft t o roll over to the right to an inverted position.

“The entire thrust of the investigation was focused on uncovering the reason behind the apparently unrecognized descent t o an altitude not only below the specified MDA, but to one below the Bradford Regional Airport elevation. In the process of attempting to identify the cause of this descent, a number of factors were eliminated from consideration by the known facts. On-scene investigation of the aircraft wreckage, and subsequent detailed examination of the propellers, altimeters, and airborne navigation equipment, did not disclose any evidence of pre-impact failure of aircraft structure, control systems, powerplants, propellers, or instruments. Nor was there any indication of these or any other problems of an emergency nature in the crew’s recorded conversation….

“The remaining possibility to be considered, and one which is most consistent with the known facts, is that the descent below MDA was unintentional and unrecognized because the attention of both pilots was directed outside the cockpit and neither were observing the instruments. It is believed that this situation developed as a result of the factors discussed below, none of which was individually significant, but all of which, acting in combination, caused th e captain and first officer to be looking outside the aircraft at the same time to establish visual reference to the ground at a critical stage in the descent….” (NTSB. Allegheny Air…Bradford…Dec 24, 1968.)

Aviation Safety Network: “At 20:08:47 the flight reported that they were doing the procedure turn inbound for runway 32 and Bradford FSS told them wind was 290 degrees at 15 knots. The Convair descended in light snow showers until the aircraft contacted trees along terrain which had an average upslope of 1.5 degrees some 2.5 n.m. short of the runway. The airplane cut a swath through the trees and impacted the ground at a point 800 feet from the initial tree contact. The fuselage came to rest inverted.”

“On January 17, 1969 safety recommendations were issued to the FAA regarding approach and landing accidents in poor weather conditions. The NTSB… recommended expediting development and installation of audible and visible altitude warning devices and the implementation of procedures for their use. The FAA replied that a rule became effective on September 28, 1968, which will require by February 28, 1971, both visual and aural altitude alerting signals to warn pilots of jet aircraft when approaching selected altitudes during climbs, descents, and instrument approaches. The FAA also reported that an Instrument Landing System (ILS) was installed at the Bradford Regional Airport in the fall of 1969.” (ASN. Allegheny Air Flight 736, 24 Dec 1968; cites NTSB/AAR-70-04, 28 Jan 1970)

Sources

Aviation Safety Network. Accident Description. Allegheny Airlines Flight 736, 24 Dec 1968. Accessed 3/2/2009 at: http://aviation-safety.net/database/record.php?id=19681224-0

Kimura, Chris Y. World Commercial Aircraft Accidents 3rd Edition, 1946-1993, Volume 1: Jet and Turboprop Aircrafts. Livermore, CA: Lawrence Livermore National Laboratory, Risk Assessment and Nuclear Engineering Group. 4-11-1994.

National Transportation Safety Board. Aircraft Accident Report. Allegheny Airlines, Inc. Convair 530, N5802, Near the Bradford Regional Airport, December 24, 1968 (NTSB-AAR-70-4; File No. 1-0033). Washington, DC: NTSB, Adopted January 28, 1970, 49 pages. Accessed at: http://www.airdisaster.com/reports/ntsb/AAR70-04.pdf