FAA studies FOD detection systems

 - September 23, 2008, 6:17 AM

The FAA has begun trials of four separate systems designed to automatically detect, report and pinpoint the location of foreign objects on airport runways. The purpose of the trials is to examine the capabilities of different technology approaches to the problem, and to embody the results in an Advisory Circular in mid-2009.

How serious a problem is foreign object debris (FOD)? The one unforgettable FOD-caused accident was the loss in 2000 of an Air France Concorde when, during takeoff, one of its tires struck a 16-inch titanium strip that had fallen from a previously departing aircraft. Impact pressure from a piece of the disintegrating tire burst one of the SST’s fuel tanks, leading to a massive fire from which recovery was impossible.

There have been no FOD-related aircraft losses since then, but the threat has not receded. In fact, some years ago Boeing estimated the annual worldwide costs of FOD damage to airliners as more than $4 billion. Recently, it has been suggested that those costs could now be as high as $12 billion when all factors, including repair of damaged tires, fuselages and, most expensively, engines, plus flight delays and aircraft out-of-service costs are considered.

FOD can be virtually anything that lies on the runway that can be struck by–and has the potential to damage–an aircraft during takeoff or landing. Mechanics’ tools, aircraft chocks, broken pieces of runway pavement and even airframe or engine parts have been found on runways. At Vancouver International, a length of fuel truck grounding cable was recovered from one of the runways; whipped up into the propeller of a small aircraft, the cable could have spelled disaster. Impact speed is also a key factor: the metal strip that downed the Concorde would probably have caused little damage if the airplane had been taxiing.

Current Detection Systems
Today, runways are inspected by periodic vehicle patrols, which pick up visible FOD items. While this approach is fairly effective, it has several disadvantages. Generally, the patrol must cover the length of the runway reasonably quickly, making detection of small items difficult. Also, patrols are restricted during busy periods.

FOD items can also appear on the runway soon after the inspection vehicle has passed or, as in the Concorde accident, fall from an arriving or departing aircraft just minutes before the arrival or departure of another aircraft. And finally, of course, objects on the runway are much harder for a human observer to see in low visibility or at night.

At Vancouver, four continuously operating automatic radar-based FOD detection systems have been monitoring the airport’s two main runways since February 2007, where they augment the traditional, four-times-per-day, manned vehicle patrols. During that time, the vehicle patrols detected 61 objects, while the automatic system detected 265.

So far, FOD has not been a major problem for corporate aviation. Possibly, this has been due to the location of the engines on most business jets–higher than on airliners–coupled with their lower ability to suck debris up off the runway surface. However, the tires of corporate aircraft are always vulnerable, as are pressurized fuselage skins struck by objects thrown up from the undercarriage.

Nevertheless, the problem clearly arises with the larger, lower-slung and more powerful engines of airliner derivatives such as the BBJ and ACJ, and with their operation into smaller, less well maintained airports, particularly at some overseas locations.

The FAA’s Technical Center at Atlantic City is conducting the current tests, with technical support and data analysis provided by the Center of Excellence for Airport Technology (CEAT) at the University of Illinois. The following systems are under test:

• Tarsier by QinetiQ, UK. The system uses millimeter wave radars and high-resolution cameras, mounted on rigid towers. It is under test in Providence, R.I.

• iFerret by Singapore-based Stratech. The system uses high-resolution cameras, mounted on rigid towers and is under test at Chicago O’Hare.

• FOD Finder, by Trex Enterprises of San Diego, is under test at Chicago Midway and O’Hare. The system uses millimeter wave radar and an infrared camera, mounted on the roof of an airport vehicle.

• FODetect by Israel-based X-Sight uses high-resolution cameras and millimeter wave radars, mounted on runway edge lights. It is being tested at Boston Logan.

Individual manufacturers’ briefings on all four systems were part of a special FOD session at a recent three-day NextGen Symposium presented in Louisville by the American Association of Airport Executives. The session also included an FAA overview of its evaluation process, where program manager Jim Patterson emphasized that the agency was not attempting to choose the best of these four systems. Rather, its goal is to evaluate their different technologies and design approaches over a 12-month period, with primary emphasis on winter operations where snow can obscure small, but still dangerous, debris.

Remote Inspection Capability
The manufacturers of the three fixed systems described their FOD-detection methods, and their provision of immediate alerts to airport tower and other personnel, together with the way their different camera techniques allow personnel to remotely inspect objects to determine their potential hazard. Remote visual inspection is important; a windblown paper bag could otherwise be mistaken for a large, high-risk object and cause unnecessary delay in busy departure and arrival activity while an inspection team was dispatched to determine its nature. Birds or small animals stopping briefly on the runway could have the same effect, since the systems should ideally be able to detect objects as small as two-inch steel bolts and metal washers.

Consequently, the trials will assess the performance of each system against a range of criteria developed jointly by FAA and CEAT researchers, the goal being to create national standards for automatic FOD detection systems. All systems must complete their winter test this year and early next year, since a draft technical note on the CEAT’s technology evaluations is planned for early next spring, followed by a draft Advisory Circular by mid-year. The FAA also intends to add FOD detection systems as qualifying for Airport Improvement Program funding.

The FAA is not alone in its FOD detection activity. In fact, the UK launched an investigative program shortly after the Concorde accident, and the British Tarsier system is the result of that work. U.S. and foreign military forces have also had long-standing “FOD walk” runway inspections before flight operations. In addition, Eurocontrol has a FOD Working Group–including U.S. and Canadian participation–that has produced general requirements for automatic detection and reporting systems and will begin trials shortly.

FOD may never be totally defeated on every runway worldwide. But the growing number of detection systems now in service worldwide, coupled with ongoing technology developments, indicate progress.