Boeing 737 TC-TLA

Summary

On 14 June 2009 at about 18:17 local time, a Boeing 737 registered TC-TLA, operated by Tailwinds Airlines, was involved in an incident near Diyarbakir, Turkey. 2 people were on board and 2 had minor injuries. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

14 June 2009 at 18:17

Classification

Incident

Location

Diyarbakir, Turkey

Nearest airport

Diyarbakir Airport (LTCC)

Coordinates

37.8926, 40.1998

Aircraft

Boeing 737

Registration

TC-TLA

Category

Airplane

Engines

2

Operator

Tailwinds Airlines

Operating rule

Non-U.S., Commercial

Phase of flight

Not recorded

Route

Istanbul → Diyarbakir

Aircraft damage

Not recorded

Weather

VMC

Light

Not Reported

NTSB number

ENG09IA011

2 people had minor injuries.

An uncommanded elevator surface deflection as a result of a left elevator PCU input arm assembly jam due to FOD lodged between the input arm assembly and the PCU housing. The FOD was a roller element from an elevator upper torque tube output crank bearing, but how or when the roller element liberated from its bearing assembly could not be determined. Contributing to the survivability of this incident was the flight crew’s immediate actions in response to the elevator control system jam.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The Boeing 737-400 airplane experienced an uncommanded pitch up event at 20 feet radio altitude during landing. The flight crew reacted to the uncommanded pitch-up event by adjusting the stabilizer trim position, attempting to move the elevator control columns forward, disengaging the autothrottle, and executing a go-around. The airplane subsequently landed without incident and both crewmembers sustained minor injuries that were incurred during the go around. Post-incident inspection of the elevator Power Control Units (PCUs) revealed that the left elevator PCU input control arm assembly was jammed by a piece of Foreign Object Debris (FOD) in a position that offset the control arm in a downward direction. With the control arm deflected in this direction and with hydraulic pressure on, the left PCU moved the elevators to a position that pitched the airplane nose up independent of pilot input. An assessment of information obtained from the FDR regarding the functional characteristics of the airplane’s pitch control system indicates that the elevator control system was fully functional and operated as designed during previous flights and up until the uncommanded pitch event occurred. According to Boeing, a jam in either the left or right PCU input control arm assembly could result in the loss of manual control of both elevator PCUs under hydraulic-powered operation. The flight crew’s immediate actions of exerting constant and excessive force on the control columns and executing a go-around at low altitude following the jam resulted in recovery of airplane pitch control despite high control forces. Metallurgical analysis revealed that the FOD had the same dimensions and material composition as the metal rollers that are contained in a DAS10-26B1-502 bearing, which is installed in only two locations in the aft elevator control system; the right and left ends of the elevator upper output torque tube crank assembly. Post-incident inspections of the airplane’s elevator system components located within the area of the tail cone also revealed that the left hand elevator upper torque tube output crank bearing/sleeve was completely intact with all rollers present. Examination of the maintenance records revealed that the left elevator upper torque tube output crank bearing/sleeve assembly had been replaced in January 2009 to correct an elevator freeplay discrepancy on the incident airplane. However, based on the available information, it could not be determined whether the metal rollers were left behind following the maintenance work performed in January 2009 or were present before the work was performed.

Quoted verbatim from the NTSB record.