Introduction
Per the Federal Aviation Administration (FAA), foreign object debris (FOD) is defined as “any object, live or not, located in an inappropriate location in the airport environment that has the capacity to injure airport or air carrier personnel and damage aircraft.” When FOD interferes with aviation operations in a manner that causes damage, it is often called foreign object damage (also abbreviated as FOD). This paper will utilize the former definition, although the terms can be used somewhat interchangeably. FOD has caused countless aviation-related incidents, including a significant number affecting Department of Defense (DoD) aircraft.1
This paper will provide a brief overview of FOD and the potential impacts to aviation operations. Additionally, this paper will briefly examine the policies, precautions, and equipment that are currently available in order to mitigate the effects of FOD. Finally, the paper will examine two (2) recent case studies involving FOD-related mishaps affecting DoD aircraft.
FOD Overview
FOD can come in a variety of forms. Tools, nuts/bolts, and other maintenance-related items are required for aircraft maintenance and are ubiquitous in hangars and throughout airfields. Maintainers, flight crew, and airfield personnel also have a number of personal items (such as cell phones, wallets, identification badges, hats, sunglasses, and pens) that could potentially be dropped/misplaced in airframes, maintenance areas, or on the flightline. Small FOD items can also be introduced to airfields via the treads of tires on vehicles entering the airfield area. Items located off of the airfield (such as vegetation or garbage) could also be blown onto the airfield, creating a FOD hazard.1
A primary FOD concern is the presence of birds and other wildlife. A well-publicized incident involving bird strikes was the 2009 water landing of US Airways Flight 1549 by pilot Captain Chesley “Sully” Sullenberger on the Hudson River in New York. Prior to the water landing, the aircraft had struck a flock of geese, resulting in the loss of both of its engines. During a 24-year period from 1995 to 2019, the U.S. Air Force experienced over 100,000 wildlife strikes, resulting in 27 fatalities, the loss of 13 aircraft, and over $800 million in damages. Per the FAA, over 90% of reported bird strikes occur at or below 3,000 feet above ground level (AGL), though strikes at higher altitudes are common when birds are migrating, with ducks and geese frequently observed up to 7,000 feet AGL.2,3,4
A related emerging concern is the potential for events similar to bird strikes involving small drones which are frequently flown by hobbyists and commercial entities. In September 2017, the first confirmed incident of a drone colliding with an aircraft in the U.S. occurred in New York. In the incident, a U.S. Army Black Hawk helicopter was operating in support of security for the U.N. General Assembly when it collided with a DJI Phantom drone, resulting in damage to the helicopter’s rotor and one of its doors. Drone-related incidents are likely to continue and may increase in frequency as the technology continues to proliferate.5
Inadequate maintenance of paved surfaces on airfields (as well as the effects of geological and meteorological hazards) can lead to pavement degradation, creating FOD concerns. When concrete or asphalt ages and/or is subjected to hazards such as extreme heat/cold or flood events, it can crack and create fragments that can become a FOD hazard. DoD aircraft with vertical takeoff and landing (VTOL) capabilities such as the F-35B variant and the V-22 Osprey can accelerate the degradation of paved surfaces, exacerbating this hazard. By design, these aircraft create high heat and jet blast oriented toward paved surfaces in order to takeoff and/or land, requiring specialized concrete to mitigate pavement damage and related FOD concerns.6,7
Some meteorological factors can also be considered to be forms of FOD. Snow and ice can affect aircraft similarly to other types of FOD. Likewise, sandstorms/dust storms driven by high winds can create FOD concerns. Volcanic eruptions can create ash clouds that severely disrupt aviation activities due to safety concerns.1,8,9
While the above categories of FOD are not all-inclusive, they provide a basic overview of some of the primary sources of FOD.
FOD Impacts
FOD impacts may occur at various phases of flight, to include taxi, takeoff, mid-flight, and landing. Additionally, FOD-related incidents can occur during ground testing activities, or when an aircraft is being powered up or shut down.
Jet-powered aircraft may ingest FOD directly into engines or air intakes, while propeller-driven aircraft can sustain damage to propeller blades or other components. Helicopters can experience similar damage to rotors. FOD can damage windscreens/canopies on various types of aircraft, obstructing pilot visibility and potentially causing temperature or pressurization shifts that pose a risk to life safety. Flight control surfaces could potentially be affected by FOD, affecting the aircraft’s ability to properly and safely maneuver. FOD can also affect the landing gear assembly or tires on aircraft, preventing safe takeoff and landing.
Though the above list is not all-inclusive, it highlights some of the impacts FOD can have on various forms of aircraft. Any of these scenarios could result in damage to the airframe and/or loss of systems that directly affect flight safety, potentially leading to damage to aircraft/ground infrastructure, as well as injury and/or death.
FOD Mitigation
The DoD currently employs a number of different policies, precautions, and equipment in order to mitigate the hazard posed by FOD. During maintenance activities, it is advised that personnel remove personal items from pockets as well as worn items such as rings and watches. Tool/part accountability is also paramount during maintenance activities, as one of this paper’s case studies will show. Pens and other office supplies may also become FOD hazards in maintenance areas. “FOD walks,” in which personnel conduct a visual FOD sweep on foot, can be an effective practice. Additionally, FOD bins can placed in convenient areas in order to provide receptacles for safe disposal of FOD.10
The FAA encourages airfields to utilize land use planning, habitat management, and landscaping efforts in order to mitigate the hazard posed by birds and other wildlife. The U.S. Air Force utilizes weather radars to detect and monitor bird activity as a preventative measure. A variety of countermeasures are available to deter and/or disperse wildlife. Passive measures include decoy birds, bitter-tasting substances and audio broadcasts of bird distress calls. More active dispersal methods include the use of dogs, pyrotechnics/cannons, remote-controlled vehicles, and lasers. Some airfields use less-lethal methods such as paintballs and plastic projectiles in order to disperse wildlife, while some airports have employed live ammunition to hunt birds that pose a hazard to aviation.11, 12, 13, 14
Various commercial products are also available to mitigate FOD hazards. Towable runway sweeping devices are available. Vehicle-mounted blower devices utilize turbines to blow high-pressure air that removes FOD from surfaces. FOD mats are available to remove FOD from tires on vehicles entering the airfield perimeter.15, 16, 17
An effective FOD management program utilizes a combination of training, policies, and equipment in order to mitigate the hazard posed by FOD. Additionally, it should be noted that the acquisition and employment of aforementioned technologies can vary by installation and military branch. Moreover, DoD aircraft routinely utilize non-DoD airfields, which also may have varying FOD management programs. While no program or piece of technology is 100% effective, a multi-layered approach can address the various sources of FOD in order to achieve an acceptable level of FOD mitigation.
Case Study: 2023 F-35 Incident at Luke AFB, AZ
On 15 March 2023, an F-35 undergoing maintenance at Luke Air Force Base (AFB) in Arizona experienced FOD-related damage. In the incident, “abnormal noises” were heard during a ground engine test. Further investigation revealed that maintenance personnel left a handheld flashlight on the lip of an intake, which was then ingested into the engine. While no injuries were reported, damage was noted to the F-35’s “second stage rotor, third stage rotor, fifth stage rotor, sixth stage rotor, fuel nozzle, bypass duct, high pressure compressor, high pressure turbine and fan inlet variable vane,” resulting in nearly $4 million in damage. According to media reports, the damage was so extensive that the aircraft could not be repaired locally.18, 19
The investigation into the incident found that maintenance personnel had all necessary qualifications, and drug/alcohol testing of personnel came back negative. Instead, the incident was attributed to a failure to clear the inlet of foreign objects, as well as a failure to complete required checklists (to include tool accountability). The report also cast some blame on “complacency” related to the F-35’s “unnecessarily lengthy” maintenance checklists, as well as a lack of network connectivity on the flightline.18, 19
Case Study: 2022 T-38 Crash in Mississippi
On 07 November 2022, a T-38 trainer aircraft crashed shortly after takeoff near Columbus Air Force Base in Mississippi. The pilot ejected from the aircraft and was taken to a local hospital with minor injuries. A subsequent investigation revealed that a “large’” bird collided with the aircraft’s canopy. Fragments from the canopy (and potentially pieces of the bird) were then ingested into both of the T-38’s engines. One engine failed outright, while the other was only able to produce reduced thrust inadequate to safely maneuver the aircraft. The investigation found that the incident was “unavoidable,” and was handled well by the experienced pilot. Columbus AFB “was following regular bird strike prevention and awareness protocols at the time of the mishap, and the pilot knew the risk that birds posed to his jet,” according to the Air Force’s report on the incident.20, 21
Outlook
FOD-related incidents will continue to affect DoD aviation activities due to the various causes and sources of FOD, the unpredictability of such incidents, and the varying effectiveness of countermeasures. RMC’s Intelligence and Climate Analysis Division continues to monitor and assess aircraft mishaps involving the DoD, to include those caused by FOD hazards. Additionally, RMC’s transportation subject matter experts maintain the capability to conduct detailed assessments of airfield infrastructure, to include potential FOD hazards.
Sources
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