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Air Safety Advisory Letter A20P0071-D4-A1

200 Promenade du Portage
Place du Centre, 4th floor 
Gatineau, QC K1A 1K8 

09 November 2020

Director General, Civil Aviation
Transport Canada

Re :

Air Safety Advisory Letter A20P0071-D4-A1
Cessna 120 and 140 aircraft lap belt centre mounting bracket failure

On , 2 pilots on board a privately registered Cessna 140 aircraft (registration C-GOFK, serial number 11313) were conducting a recreational flight from an abandoned airstrip at the north end of Stave Lake, British Columbia (BC), to Pitt Meadows (CYPK), BC. During a take-off attempt, the aircraft did not become airborne and the takeoff was aborted. While braking, the aircraft rapidly nosed over and came to rest inverted. One pilot was fatally injured, while the other sustained minor injuries. The investigation A20P0071 is ongoing.

The lap belts of Cessna 140 aircraft are anchored to the aircraft at 2 locations for each seated position; on each side outboard of the seats and to a common centre bracket that has individual attachment arms for each of the 2 belted positions. The investigation found that one arm of the lap belt centre mounting bracket was broken (Figure 1). Although the Y-belt forming the shoulder harness remained attached to the lap belt, the failure of the centre bracket allowed the pilot flying to become largely unrestrained during the accident sequence. The BC Coroner has determined that the pilot flying received fatal injuries because of cervical spine trauma.

Figure 1. Occurrence aircraft lap belt centre mounting bracket (Source: TSB)
Occurrence aircraft lap belt centre mounting bracket (Source: TSB)

The aircraft’s lap belt centre mounting bracket was sent to the TSB Engineering Laboratory in Ottawa, Ontario, for metallurgical examination. It was determined that the bracket was made of an aluminum alloy and had not failed due to metal fatigue, but had rather likely failed due to overstress during the accident.

Nose-over occurrences of Cessna 140 aircraft are not uncommon. TSB records contain 21 occurrences in which a Cessna 140 aircraft has nosed over in the past 30 years. In the same period in the United States, the National Transportation Safety Board (NTSB) recorded 42 Cessna 140 aircraft nose-over occurrences. A 2014 NTSB investigation (ERA14FA327) found that the aluminum alloy lap belt centre mounting bracket of a Cessna 140 aircraft failed due to shearing overstress during a nose-over accident in Parma, New York. This resulted in the pilot becoming unrestrained during the accident sequence. The pilot’s head contacted the overhead area of the cockpit interior resulting in cervical spine trauma.

Cessna 120 and 140 aircraft shared the same lap belt centre mounting bracket design. During the manufacturing life of both aircraft types (1946 to 1951), the Cessna Aircraft Company issued an engineering drawing change notice in which the bracket material was changed from aluminum alloy (Alclad 2024-T3) to steel alloy (SAE 4130).Footnote 1  

Following the 2014 accident in Parma, Textron Aviation Inc., which is now the type certificate holder, issued a Single Engine Service Bulletin (SEB-25-03) on 17 February 2015, affecting Cessna 120 aircraft (S/N 8000 through 15075) and Cessna 140 aircraft (S/N 8000 through 15075). This required that, at the next 100-hour or 12-month (annual type) inspection, the lap belt centre bracket be inspected to determine if the latest type of bracket (in steel alloy) was installed, and if not, to replace the aluminum bracket with the steel one (P/N 0425132). Two months later, on 15 April 2015, the Federal Aviation Administration issued a Special Airworthiness Information Bulletin (SAIB CE-15-13) to alert owners, operators, and aircraft maintenance technicians of its airworthiness concern with the aluminum lap belt centre mounting bracket.

A review of the Transport Canada (TC) aircraft registry database found that 208 Cessna 140 and 79 Cessna 120 aircraft are currently registered in Canada. Of these, 142 (68%) of the Cessna 140 and 57 (72%) of the Cessna 120 aircraft were manufactured before the change from aluminum to steel alloy became effective.

This latest occurrence demonstrates that without the incorporation of the steel alloy lap belt centre mounting bracket in Cessna 120 and 140 aircraft, failure of the aluminum centre bracket during accidents may continue, thus increasing the risk of potentially fatal injuries. TC may wish to consider safety action for the lap belt centre mounting bracket for all affected Cessna 120 and 140 aircraft.

The TSB would appreciate being advised of any action that is taken in this regard.

Upon the completion of investigation A20P0071, the Board will release its investigation report into this occurrence.

Yours sincerely,

Original signed by

Natacha Van Themsche
Director of Investigations — Air
Transportation Safety Board of Canada