ASN Wikibase Occurrence # 16282
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| Date: | Saturday 22 March 2008 |
| Time: | 09:00 LT |
| Type: |  Boeing 757-225 |
| Owner/operator: | US Airways |
| Registration: | N921UW |
| MSN: | 22201/21 |
| Year of manufacture: | 1983 |
| Fatalities: | Fatalities: 0 / Occupants: 180 |
| Aircraft damage: | Minor |
| Category: | Serious incident |
| Location: | near Annapolis, MD -
 United States of America
|
| Phase: | En route |
| Nature: | Passenger - Scheduled |
| Departure airport: | Orlando International Airport, FL (MCO/KMCO) |
| Philadelphia International Airport, PA (PHL/KPHL) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
A US Airways Boeing 757-200, flight number 1250, registration N921UW, lost a left upper wing trailing edge panel during cruise flight at FL270. Initial reports were that the flight crew had experienced "light chop" at the time. The flight was enroute from Orlando International Airport, FL (MCO) to Philadelphia International Airport, PA (PHL). The panel struck the window of passenger row 19ABC and cracked
only the outer portion of the window. Pressurization was not lost. The flight crew continued on to PHL.
Upon approach to PHL the flight crew informed ATC that they could not increase their airspeed due to
possible airframe damage. The flight landed uneventfully. There were 174 passengers and 6 crew
members on board with no reported injuries.
NTSB materials laboratory examined the wing-side portions of the left wing trailing edge panel clips from the inboard, middle and outboard positions, with fasteners. Analysis indicated that the wing panel clips fractured due to fatigue. The fatigue region of the inboard clip covered the largest area fraction and was smoothest among the three clips, indicating that fatigue initiated first in the inboard clip. No evidence of corrosion or material anomalies was observed at the fatigue origin. The shape of the fatigue crack in this clip is consistent with fatigue crack propagation primarily under out-of-plane (inboard-outboard) bending loads.
Boeing Service Bulletin (SB) 757-57-0027 was issued April 28, 1988, to address fatigue cracking of attach clips at the location of the fracture in the incident airplane clips. Thickness of the middle clip from the incident airplane indicates that the clips were replaced using kit number 012N8546-1 clips. However, the clips were installed on the incorrect side of the vertical stiffener, and the clips were not installed with spacers as required in SB. Installing the clip on the outboard side of the rear spar vertical stiffener instead of the inboard side would be expected to put additional tensile stress on the inboard side of the clip, which is where fatigue initiation was observed. It is likely that this incorrect installed increased stresses on the clips, which would increase the likelihood of failure due to fatigue.
Patterns in the sealant and filled holes on the inboard clip indicate that it was repositioned to a lower position at some time. The middle clip showed sealant filling areas where the white paint was missing, indicating that the middle clip might have been removed and reinstalled at some time as well.
Probable Cause: The installed wing panel clips failed due to fatigue, likely caused by the incorrect installation of the fasteners in response to SB 757-57-0027. Contributing to the incorrect installation was the SB's lack of clarity in the instructions and figures on the correct orientation of the clips and spacers.
Accident investigation:
 |
|
Sources:
NTSB DCA08IA048
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 23-Mar-2008 11:56 | relax630 | Added |
| 28-Mar-2008 05:05 | harro | Updated |
| 21-Dec-2016 19:13 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
| 21-Dec-2016 19:14 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
| 21-Dec-2016 19:16 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
| 21-Dec-2016 19:20 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
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