This report was originally released on 1 April 2011; however, it was subsequently discovered that not all of the directly involved party responses had been considered before the report was approved for release. Those comments have now been considered and this version amends the previously released final report.
On 7 May, 2010, at about 1458 Eastern Standard Time (EST), a Boeing 747-422 aircraft, registered N128UA was being operated on a regular public transport flight from Sydney, Australia to San Francisco, USA. Shortly after conducting a reduced-thrust takeoff, the crew was advised by Sydney Air Traffic Control that the aircraft had sustained a ground strike. After completing the appropriate checks and dumping fuel, the crew returned the aircraft to Sydney and landed. A subsequent inspection revealed scrape damage to the aircraft's lower rear fuselage consistent with contact with the runway surface.
Analysis of recorded flight data by the aircraft manufacturer indicated that the aircraft was subject to a wind gust during rotation. That, combined with a high instantaneous pitch rate around the time of lift-off and a reduction in lift due to spoiler deployment, reduced the tail to runway clearance. Another contributing factor was the reduced-thrust takeoff, which increased the aircraft's exposure to wind variations during rotation. The manufacturer also noted that, had the crew applied a smaller left control wheel input at an earlier stage of the takeoff, it was possible that the spoilers would not have deployed, resulting in a small increase in tail clearance.
Although the investigation did not identify any organisational or systemic issues that might adversely affect the future safety of aviation operations, following the occurrence, the aircraft operator revised its flight manual for the 747-422.