Accident underscores FOD threat

 - December 27, 2007, 9:44 AM

A November airline takeoff incident in South Africa, reportedly involving foreign object damage (FOD), has attracted the attention of aviation safety officials worldwide and could be of concern to corporate operators of aircraft with powerful low-slung engines, such as the Boeing BBJ and 757/767 and the Airbus ACJ.

In the incident, the crew of a Nationwide Airlines Boeing 737-200 heard a loud bang as they rotated for liftoff at the Cape Town airport and, with an apparently failed starboard engine, climbed straight ahead. In the passenger cabin, a window-seat occupant reportedly told his companion, “Look, the engine just fell off.” And indeed it had, taking the pylon with it. The crew continued the climb and, after circling to burn off fuel, performed an uneventful engine-out landing.

Subsequently, Nationwide stated that preliminary investigations showed the engine had detached because of severe engine vibrations after it had ingested an object on the runway while at maximum power during takeoff. An airline official pointed out that the pylon-to-wing supporting structure was designed to release the engine under such circumstances to prevent structural damage to the wing.

The incident has refocused attention on FOD events, which are more common than is generally believed. Unofficial estimates place annual FOD costs in repairs, out-of-service time and schedule disruptions for at around $20 million per major airline.

Arguably the worst FOD accident on record was the July 2000 crash of an Air France Concorde at Paris Charles de Gaulle, when a 16-inch-long titanium strip lying on the runway pierced one of the airplane’s tires before liftoff. Tire shrapnel burst a fuel tank, igniting a fierce fire, and the SST struggled until, unable to accelerate or climb, it crashed.

One result of the Concorde catastrophe was the development by the UK Government’s Defence Evaluation and Research Agency–subsequently privatized as QinetiQ–of a highly accurate millimeter wave radar to detect debris on airport runways, and specifically objects smaller than the titanium strip that downed the Concorde.

Current production units, now undergoing FAA evaluation, can detect small items lying on the runway. Upon detecting an object, the radar provides its precise GPS coordinates to the runway inspection vehicle. QinetiQ has developed an advanced technology, day/night surveillance camera for the radar to minimize false alerts.

Earlier tests of the system at Vancouver, British Columbia, were successful, except on two occasions when the reported objects could not be seen immediately at the GPS position. In both cases, they were under the vehicle. Vancouver subsequently purchased four QinetiQ radars–called Tarsiers, after a Philippine primate whose eyes separately scan through 180 degrees–and these now cover the airport’s two main runways.

How much of a threat is FOD to corporate aircraft? NBAA vice president of safety and regulation Doug Carr and Peter Ingleton, IBAC director ICAO liaison agreed that historically, FOD has not been a major problem. Carr pointed out that the engines on most business jets are significantly higher above the ground than those of airline jets, while Ingleton noted that their much less powerful engines produce less suction to pull debris up off the runway surface. On the other hand, tires would always be vulnerable, as are fuselages struck by objects thrown up from the undercarriage. But there is little data on the incidence of FOD across the corporate fleet, possibly because of its relatively lower flying hours and therefore reduced per-airplane exposure to the risk.

Nevertheless, the risk clearly exists for the larger, lower-slung engines of the airliner derivatives now entering corporate aviation in increasing numbers, and with the operation of these aircraft into smaller, less well maintained airports.