Loose and cracked screws in the trim tab system have become the focus of a US federal investigation into the 16 September 2011 crash of a modified P-51 at the Reno Air Races in Nevada, that killed 11 people and injured more than 60.
The US National Transportation Safety Board (NTSB)on 21 August released hundreds of pages of material documenting the ongoing probe into the crash of the modified P-51 - the "Galloping Ghost".
The P-51 crashed into a crowd of race fans after the pilot lost control immediately after the right and left trim tabs separated from the aircraft.
NTSB has not released any conclusions, but the new documents show investigators have focused on two possible explanations for the crash.
Screws attaching the trim tabs to the control rods are the common link between both possible explanations.
A materials laboratory factual report on the wreckage of the aircraft discovered a growing screw fatigue crack and loose screws in the trim tab system.
An aircraft performance study completed on 20 August concluded that such a condition could have led to a low-amplitude flutter that overloaded the control rod for the trim tabs until it failed.
Alternatively, the aircraft could have encountered the wake from another aircraft, which aggravated the flutter condition triggered by the loosened screws.
The wake encounter alone is unlikely to have caused the control rod to break, the NTSB says. The crash prompted the NTSB earlier this year to slam the Federal Aviation Administration for having inadequate guidelines for safety at air shows and air races.
Source: Flight International
