What Is an Automated FOD Detection System?

What Is an Automated FOD Detection System?

An automated FOD detection system is a set of sensors that finds foreign object debris on airfield pavement and alerts the airport operator.

FOD stands for foreign object debris. ICAO and EASA define it as an inanimate object within the movement area. It has no operational or aeronautical function and can be a hazard to aircraft operations. The FAA defines FOD as any object, live or not, in an inappropriate place that can injure people or damage aircraft. FOD includes fasteners, tools, tyre fragments and pieces of concrete or asphalt.

A named case is the Concorde crash of 25 July 2000. A Concorde tyre ran over a titanium alloy wear strip from a DC-10. That DC-10 took off five minutes earlier. Debris from the tyre hit the wing, and tank 5 ruptured.

Why FOD matters

AC 150/5220-24 lists three kinds of harm. FOD can cut aircraft tyres. It can enter engines. It can lodge in mechanisms that affect flight operations. Jet blast can also propel FOD at high speed and injure people.

How the sensors work

The FAA defines the sensor types by their primary means of detection:

• A radar system transmits and receives radio signals to detect objects.
• An electro-optical system uses visible light. It analyses the camera data with image processing, which is digital analysis of the sensor data.
• A hybrid system uses data from both a radar and an electro-optical sensor.
• A mobile radar is a radar on a vehicle that scans the surface in front of it.

The AC does not limit the technology that an airport may use. It does not mention artificial intelligence. The AC lists the characteristics of the systems on the market in 2009 and gives performance requirements that any technology must meet.

System types

FAA AC 150/5220-24 (2009) names four types. The table gives the characteristics of the systems on the market at that time.

Fixed systems give continuous surveillance. Mobile systems supplement human inspection.

What the FAA requires

AC 150/5220-24 sets minimum performance for equipment:

• The system must detect the reference cylinder and a golf-ball-size sphere, and 90 percent of a group of typical FOD items.
• It must identify two objects as separate when they are no more than 3 m apart.
• It must locate an object to within 5 m.
• False alarms must not exceed one per day for systems with visual detection and three per day for systems without, averaged over 90 days.
• Continuous systems should update generally within 4 minutes of a FOD occurrence.
• Each system must show its performance in rain, snow and at night, and keep a data record of alert time and location.
• The system must tell the airport operator about any place in the surveillance area where detection is not possible.

The runway is the primary surveillance area. Other paved movement areas have a lower priority. The AC sets a design life of at least 10 years.

Use of the AC is generally not mandatory. It is mandatory for equipment bought with Airport Improvement Program or Passenger Facility Charge funds.

What an airport weighs when it chooses a system

The AC lists the factors that an airport operator may consider:

• the number and type of aircraft
• the size and location of the surveillance areas
• the sensitivity of the equipment, because more sensitivity generally means more false alarms
• the maintenance needs of the equipment
• the climate, because heavy rain or snow can degrade sensors
• the ability of staff to respond to alerts and recover FOD

What happens after an alert

An alert tells airport staff that a sensor found an object. The user interface may sit in the airport operations centre, the maintenance centre or the control tower. The airport decides how to tell its staff to remove the FOD. It also decides how to tell air traffic control to divert aircraft if the risk is high.

FAA AC 150/5210-24A gives two cases. If the FOD is not an immediate hazard, remove it as soon as the operating schedule permits. If it is an immediate hazard, the FOD programme must let an airport supervisor stop operations for a time. The FAA recommends that airports agree procedures for this with their air traffic control facility.

The airport should record how it detected each FOD item, when and where, what it was, and its possible source. The FAA invites airports to submit data on type, location and source to the national FOD database.

Does the system replace the inspection?

No. FAA guidance states that FOD detection systems are not designed or certified as safety critical systems. Airports cannot use them in place of required inspections. An airport that has one can use its other functions, but only in a supplemental, advisory way.

ICAO Annex 14 requires daily inspections of the movement area. It requires at least two for aerodrome code number 3 or 4. FAA AC 150/5220-24 calls airport personnel the primary sensor for FOD.

FOD checks without automation

The inspection is the base of every FOD programme. These are the main practices:

• Inspect the movement area at least once a day, and more often in construction areas and after an accident, incident or spill. EASA adds inspections after extreme weather.
• Make two or more passes along a runway to reduce the width of each inspection zone. Drive the stub taxiways, because inspectors often overlook them.
• Inspect on foot to reach areas that a vehicle cannot, such as grass.
• Use extra lights on vehicles for night inspections.
• Let tenants and air carriers join the inspections and report FOD that they see.

Some airports run FOD walks. Staff, partners and volunteers collect FOD by hand. The FAA notes that these walks do not always record the location and origin of each item.

What the FAA found in tests

The FAA tested four types of system to set the minimum performance requirements. The reports are:

• a radar system at Providence, DOT/FAA/AR-10/33
• an electro-optical system at Chicago O’Hare, DOT/FAA/AR-11/13
• a hybrid system at Boston Logan, DOT/FAA/TC-12/22
• a mobile radar system at three airports, DOT/FAA/AR-11/12

In a later FAA study at Boston Logan, the FAA compared a runway with a hybrid system to a runway with human inspection only. Over 18 months, the system found 139 objects and people found 21. Of the 139, 95 were wildlife carcasses. At Seattle-Tacoma, over 12 months, the system found 102 objects and people found 30. Of the 102, 37 were wildlife carcasses. The FAA also notes concern about the number of false positives.

Drones and AI cameras

The AC defines image processing but not artificial intelligence. The FAA tested a small unmanned aircraft with a deep learning algorithm. The tests took place at Cape May County Airport and Atlantic City International Airport. The workflow detected 96 percent of the FOD items that the AC specifies. It met only some of the AC requirements. It needs work on false positives, processing time, an alert interface, and detection in low light and bad weather.

Where FOD comes from

The AC lists personnel, airport infrastructure (pavements, lights and signs), the environment and equipment as sources. The AC cites a one-year airport study. Over 60 percent of the items were metal, 18 percent were rubber, and nearly 50 percent were dark-coloured. Typical items from the pavement are concrete and asphalt chunks, rubber joint material and paint chips.

AC 150/5380-6C notes that pavement distress can generate loose material that strikes propellers or enters jet engines. It says all pavement inspections should address FOD. AC 150/5210-24A names deteriorating pavement with spalling or cracks as a source. It adds that tests show cracks and joints are the main sources of ingested foreign objects. It asks airports to clean them.

Cost

The FAA briefing on the Boston Logan study gives an installation cost of about 1.7 million US dollars for 7,000 ft of runway 9/27. The FAA cost-benefit analysis, DOT/FAA/TC-22/47, reports that estimates of the annual global cost of FOD range up to 22.7 billion US dollars. Neither figure is a price for another airport.

Rules

EASA ADR.OPS.B.016 requires the aerodrome operator to run a FOD control programme. The programme includes procedures to detect FOD by monitoring and inspecting the movement area to a schedule. It also requires data collection to find FOD sources and trends. ICAO Annex 14 requires daily inspections of the movement area and the monitoring of pavements to avoid FOD. Neither paragraph requires an automated system.

In the United States, 14 CFR 139.305(a)(4) requires prompt removal of mud, dirt, sand, loose aggregate, debris, foreign objects, rubber deposits and other contaminants. The removal must be as complete as practicable. Section 139.327 requires daily inspections at certificated airports. AC 150/5210-24A describes those inspections as the main means of FOD detection at some airports.