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Accident description
Last updated: 23 June 2018
Status:Final
Date:Friday 21 September 1990
Time:09:25
Type:Silhouette image of generic B703 model; specific model in this crash may look slightly different
Boeing 707-336C
Operator:Air Hong Kong
Registration: VR-HKK
C/n / msn: 20517/854
First flight: 1971-05-18 (19 years 4 months)
Crew:Fatalities: 0 / Occupants: 3
Passengers:Fatalities: 0 / Occupants: 2
Total:Fatalities: 0 / Occupants: 5
Aircraft damage: Substantial
Aircraft fate: Repaired
Location:Sydney-Kingsford Smith International Airport, NSW (SYD) (   Australia)
Phase: Pushback / towing (PBT)
Nature:Cargo
Departure airport:Sydney-Kingsford Smith International Airport, NSW (SYD/YSSY), Australia
Destination airport:?
Narrative:
The Boeing 707 cargo aircraft was being prepared for a normal push-back from the freight apron position V2 at Sydney-Kingsford Smith Airport, Australia.
A towing tug was connected to the nose gear and number two engine was running at idle power. The aircraft was cleared to be pushed back to taxiway G where the other engines would be started. The aircraft brakes were released but as the tug took the weight for the push back, there was a loud report and the nose of the aircraft collapsed onto the cabin roof of the tug. The nose wheels folded back under the fuselage and arrested its fall, saving the tug cabin from further collapse. The engine was immediately shut down and the crew departed the aircraft to assess the damage. Investigation revealed the nose landing gear oleo outer cylinder
had failed at the upper end of the cylinder bore. The failure was initiated by a fatigue crack in the radius at the bore end forward quadrant. The radius in the vicinity of the crack was found to be .039 inches, marginally less than the manufacturer's minimum dimension of .040 inches. Extension of the crack due to stress corrosion was extremely rapid and may have occurred whilst the aircraft was parked at Sydney.

Probable Cause:

Significant Factors:
The following factors were considered relevant to the development of the accident
1. A fatigue crack developed in the bore top radius of the nose landing gear cylinder.
2. The marginal dimension of the bore top radius may have contributed to the development of the initial fatigue crack.
3. Stress corrosion then developed the crack at a rapid rate to final failure.

Accident investigation:
cover
Investigating agency: BASI
Status: Investigation completed
Duration: 1 year and 4 months
Accident number: 199002004
Download report: Summary report

Classification:



Follow-up / safety actions
Because of numerous reports of cracking in this area, the manufacturer issued a service letter recommending that operators consider replacement of nose landing gear cylinders fabricated from 7079-T6 alloy with cylinders of 7075-T3 or 7049-T73 alloy at overhaul.

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This information is not presented as the Flight Safety Foundation or the Aviation Safety Network’s opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.
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