On January 3, 1986, a Boeing 737-2H4 (registration N86SW) was involved in an aviation accident near Dallas, TX. Investigators recorded the probable cause as: The cone bolt failed due to fatigue, most probably due to improper installation (under-torqued during engine re-installation). The safety cable failed due to overstress, probably from a rough runway. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During takeoff roll, the No. 2 engine's aft mount cone bolt failed due to fatigue from under-torquing during installation, followed by secondary support link overstress from rough runway. The engine sagged, causing thrust reverser actuator to drag runway.
Incident Overview
An incident occurred during the takeoff roll when the No. 2 engine experienced a failure of the aft engine mount cone bolt. This was followed by the failure of the secondary support link, a stainless steel cable. With both aft engine support assemblies compromised, the aft section of the engine dropped to within approximately 4 feet of the ground.
Sequence of Events
As a result of the engine sag, the No. 2 thrust reverser actuator assembly contacted the runway surface during rotation. Additionally, one leading edge flap and the forward engine fairing sustained slight damage. The aircraft subsequently returned to the airport and landed without further incident.
Metallurgical Examination
Metallurgical examination of the cone bolt revealed that it failed due to fatigue. The fatigue was most probably caused by improper installation of the bolt, specifically that it was under-torqued when the operator re-installed the engine. The safety cable failed as a result of overstress, probably induced when the aircraft encountered a rough section of runway during the takeoff roll.
Probable cause
The cone bolt failed due to fatigue, most probably due to improper installation (under-torqued during engine re-installation). The safety cable failed due to overstress, probably from a rough runway.
What happened in the 3 Jan 1986 Boeing 737-2H4 accident near Dallas, TX?
During takeoff roll, the No. 2 engine's aft mount cone bolt failed due to fatigue from under-torquing during installation, followed by secondary support link overstress from rough runway. The engine sagged, causing thrust reverser actuator to drag runway.
What aircraft was involved and where did it happen?
The accident on 3 Jan 1986 involved a Boeing 737-2H4, registration N86SW, at Dallas, TX.
What was the probable cause of the accident?
The cone bolt failed due to fatigue, most probably due to improper installation (under-torqued during engine re-installation). The safety cable failed due to overstress, probably from a rough runway.
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