It has been more than 10 years since an Air France Concorde crashed shortly after takeoff at Paris Charles De Gaulle. Fragments of an exploding tire ruptured one of its fuel tanks, creating a fierce fire that soon brought down the SST. The tire burst after striking a two-inch-wide, 16-inch-long titanium strip that had fallen onto the runway from a preceding aircraft. The strip, worth maybe $20, instantly became the costliest single piece of foreign object debris (FOD) in aviation history.
What’s the likelihood of a similar accident caused by FOD? Statistically, like Sullenberger’s bird strike, it’s extremely unlikely. In reality, either or both could happen tomorrow. FOD, like birds, remains an ever present threat. In fact, FOD impacts occur every day around the world. The reason we don’t hear about most of them is that individually, they don’t do too much damage: a cut tire, a dinged compressor blade, maybe a dent in a flap. But FOD can also be large, including mechanics’ tools, wheel chocks, pieces of concrete, broken runway edge lights and even the shattered remains of a fiberglass engine cowling. (The cowling of an Airbus A330 detached during takeoff at Vancouver in March 2000.)
Whether the foreign object is large or small, the costs to civil operators are enormous. While authorities do not keep exact records, the UK Insight SRI company has been collecting and analyzing FOD data for several years. Company principal Iain McCreary estimates that FOD damage repair, as well as delays, out-of-service time and related costs, could total around $14 billion worldwide annually. No cost estimates were available for corporate or general aviation, but with the same runway exposure, the risk levels are similar.
How do we reduce the risk? Today, inspection vehicles perform visual checks while driving along the runway, following FAA requirements of at least one inspection per day, although some airports have a two-per-day schedule. By contrast, European rules call for four daily inspections. In a presentation to the National Aerospace FOD Prevention (NAFPI) conference in St. Louis, McCreary pointed out that the problem with one daily inspection is that during the intervening 24 hours, FOD slowly accumulates along the runway to reach a peak just before the inspection. Two or four daily inspections reduce that peak, and FOD’s hazards and time on the runway, to a half or a quarter its size.
But that’s still not enough, as aircraft with much more powerful engines and higher takeoff speeds enter service. As a result, the FAA and European authorities are moving ahead with new-technology automatic FOD detection and alerting systems that can instantly detect items as small as a one-inch steel bolt that vehicle inspections can miss. Over a several-month period, Vancouver’s automatic system–installed after the A330 incident–detected 265 objects, while the vehicle patrols detected only 61 of them. This new approach to FOD is the theme of an extensive Insight SRI study called “Runway Safety: FOD, Birds and the Case for Automated Runway Scanning,” available later this year.
Since the Concorde accident, four automatic systems have been developed and have been evaluated by the FAA’s Center of Excellence for Airport Technology at the University of Illinois. All four met FAA criteria, and are each eligible for Airport Improvement Program (AIP) funding, effective October 1. One major airport in the Northeast is understood to have submitted its AIP application already.
The four systems are as different in their techniques as they are in their origins. The British QinetiQ Tarsier uses two long-range, widely separated millimeter radars positioned on towers well back from and perpendicular to the runway, to sweep its full length, with continuous camera recording. The Stratech iFerret, from Singapore, does not use radar, but instead uses up to 10 towers that carry sophisticated “intelligent” scanning cameras, also well back along the runway. The Israeli Xsight FODetect units combine millimeter radar and camera in scanning modules attached to existing runway edge lights, with airport controllers able to slew individual units laterally or vertically for optimum views. All three systems’ sensors provide day/night overlapping coverage along the full runway length. The fourth system is San Diego-based Trex Industries’ FOD Finder, which consists of a compact radome enclosing a millimeter radar and 360-degree cameras for mounting on airport vehicles, as well as a powerful vacuum for fast FOD retrieval.
At press time, QinetiQ systems had been installed at Vancouver, Heathrow and several other overseas airports, and a Stratech system has been installed at Singapore’s Changi airport. Xsight and Trex are in negotiations with several airports.
Meanwhile, governments are moving ahead on FOD legislation. The FAA last year published its first updated Advisory Circular on FOD, describing its evaluation of automatic systems and their AIP eligibility, and briefed NAFPI attendees on a second AC, due for publication on September 30, describing recommended processes to incorporate FOD data into an airport’s safety management system. In Europe, the European Commission and Eurocae have established separate FOD committees to develop standards.
FOD was on the agenda at last month’s ICAO Assembly meeting in Montreal, and the British Airports Authority is holding a Global FOD Conference next month. An international safety conference in Bangkok early next year will also review progress in new-technology FOD detection and alerting systems.
No one has any illusions that the FOD threat will one day disappear. It will always be with us, but new technology will significantly minimize its hazards.