Tailwind B734 at Liege on Jul 31st 2015, dropped flap seal plate on approach
Last Update: October 6, 2016 / 14:22:35 GMT/Zulu time
Incident Facts
Date of incident
Jul 31, 2015
Classification
Report
Airline
Tailwind Airlines
Flight number
TI-477
Departure
Bodrum, Turkey
Destination
Liege, Belgium
Aircraft Registration
TC-TLE
Aircraft Type
Boeing 737-400
ICAO Type Designator
B734
About 40 minutes after landing the crew called tower reporting the left hand inboard flap inboard seal plate was missing from the aircraft. A runway inspection did not find anything.
The aircraft departed for its next scheduled sector shortly after, about 105 minutes after landing, and continued service without interruption throughout the following days.
About 2.5 hours after landing a local resident, living under the extended runway center line of Liege's runway 05R about 3.85nm from the runway threshold, found a foreign object in his garden that was believed to be an aircraft part. Police responding to the call took the part to airport inspection services, who in cooperation with aircraft mechanics identified the part to be most likely a Boeing 737 inboard flap seal plate. The aircraft on the ground in Liege were checked, all showed their seal plates in place.
A check the following day identified TC-LTE as the aircraft missing that seal plate.
Belgium's AAIB released their final report concluding the probable cause of the serious incident was:
The in-flight and undesired detachment of the LH inboard flap/inboard seal plate was due to the failure of the attachment bolts of the pno 67279-7 plate adaptor. This was caused by the use of NAS 517 bolts instead of the Boeing-prescribed BACB30NN5K23.
The AAIU analysed that Boeing compared the properties of those two bolt types and found:
- These bolts are comparable in strength (160KSI-180KSI) and are similar in size.
- Boeing does not recommend using NAS517* instead of BACB30NN* bolts for exterior surface installations.
- BACB30NN* is a titanium aluminum pigment coated fastener.
- NAS517 fastener is a Cadmium-plated alloy steel fastener. The Cadmium plating is a sacrificial coating (A corrosion prevention method in which a metal coating is subjected to preferential corrosion as a means of protecting the substrate metal).
- There is a potential for losing the Cadmium plating, which could result in corrosion and ultimately reducing bolt strength
- The specified torque for the BACB30NN5K23 bolts in the 737 Flap plate installation is 150 in/lbs
The AAIU further reported: "Boeing engineering stated that there was no documentation generated by Boeing supporting the use of NAS517 bolts instead of BACB30NN5K23 bolts. Boeing have also reviewed the in-service communications and did not find any correspondence where Boeing allowed the use of NAS517 bolts instead of BACB30NN5K23 bolts in this installation."
Incident Facts
Date of incident
Jul 31, 2015
Classification
Report
Airline
Tailwind Airlines
Flight number
TI-477
Departure
Bodrum, Turkey
Destination
Liege, Belgium
Aircraft Registration
TC-TLE
Aircraft Type
Boeing 737-400
ICAO Type Designator
B734
This article is published under license from Avherald.com. © of text by Avherald.com.
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