Behind the Scenes at AAIB

 - May 7, 2008, 7:50 AM

The UK’s Air Accident Investigation Branch (AAIB) boasts a permanent staff of just 45 people and a seemingly modest annual budget of £4.5 million ($6.3 million). Almost three-quarters of its personnel–31 people–are accident inspectors, including four principal inspectors (two covering operations and two for engineering); 10 operations and 10 engineering inspectors; and four FDR and CVR specialists.

All AAIB operations inspectors are pilots with ATP certificates who, through an agreement with various UK airlines, fly left seat two or three days each month on scheduled flights. Between them, they specialize in all major air-transport aircraft types. Many of the engineering inspectors also hold pilot licenses, at least to private pilot level.

Each year the agency investigates roughly 400 accidents and serious incidents. As many of 80 percent of these do not involve fatalities and do not require an inspector at the accident scene. Instead, the pilots are obliged to fill out a detail form accounting for the accident and these are assessed by an inspector, who files a report within three months.

About 17 percent of accidents require a “field investigation,” with inspectors attending the accident site and publishing a report around four months later. The most serious accidents (usually no more than 3 percent of the total) require a full-scale “inspectors investigation” for which the report period spans 15 months.

AAIB maintains a roster of standby teams consisting of three pilots, three engineers and an FDR/CVR specialist who are packed and ready to attend the scene of an accident at a moment’s notice. The 1988 crash of a Boeing Chinook helicopter operated by British International Helicopters on a North Sea oil industry contract illustrated the effectiveness of AAIB’s rapid response capability.

The accident happened just before 11:30 a.m. off the coast of Scotland’s Shetland Islands. By noon, the AAIB team was en route from their Farnborough headquarters, 700 mi away in southern England. A marine salvage vessel already in the North Sea on a supply contract for Shell was commandeered, returned to shore to pick up the necessary equipment and then set sail for the accident site by 7 p.m. At around midnight, special deep-sea cables were air lifted onto the ship.

At 10:30 a.m. the following morning, the AAIB team on board the salvage vessel saw the first video shots from the seabed and immediately identified a large hole in the Chinook’s ring gear that clearly indicated metal fatigue. This was confirmed at 11 a.m. when the helicopter was brought to the surface and so, within 24 hr of the accident, the AAIB had enough evidence to warrant the grounding of the UK Chinook fleet pending safety checks.

AAIB’s flight data recorder specialists have developed their own software for visualizing accidents by computing the numerous data parameters recorded from an aircraft’s systems (1,800 on the Boeing 737-400 series, for example). The visualization system allows investigators to view a computer model of an accident from several different positions, including from above and from the cockpit. 

The AAIB is funded by the UK Department of Transport, Local Government and the Regions (DTLR) and has legally protected independence from both the Civil Aviation Authority (CAA) and the air-transport industry. Its chief inspector, Ken Smart, sends the agency’s accident reports and safety recommendations directly to DTLR secretary of state Stephen Byers, rather than through a maze of senior civil servants.