FOD Information and Prevention - What is FOD?

Foreign Object Debris (FOD) is a substance, debris or article alien to a vehicle or system which would potentially cause damage.

Foreign Object Damage (also abbreviated FOD) is any damage attributed to a foreign object (i.e. any object that is not part of the vehicle) that can be expressed in physical or economic terms and may or may not degrade the product's required safety or performance characteristics.

FOD is an abbreviation often used in aviation to describe both the damage done to aircraft by foreign objects, and the foreign objects themselves.[1][2]

"Internal FOD" is used to refer to damage or hazards caused by foreign objects inside the aircraft. For example, "Cockpit FOD" might be used to describe a situation where an item gets loose in the cockpit and jams or restricts the operation of the controls.

"Tool FOD" is a serious hazard caused by tools left inside the aircraft after manufacturing or servicing. Tools or other items can get tangled in control cables, jam moving parts, short out electrical connections, or otherwise interfere with safe flight. Aircraft maintenance teams usually have strict tool control procedures including toolbox inventories to make sure all tools have been removed from an aircraft before it is released for flight. Tools used during manufacturing are tagged with a serial number so if they are found they can be traced.

The "Damage" term was prevalent in military circles, but has since been pre-empted by a definition of FOD that looks at the "debris". This shift was made "official" in the latest FAA Advisory Circulars FAA A/C 150/5220-24 'Airport Foreign Object Debris (FOD) Detection Equipment' (2009) and FAA A/C 150/5210-24 'Airport Foreign Object Debris (FOD) Management'.

Eurocontrol, ECAC, and the ICAO have all rallied behind this new definition. As Iain McCreary of Insight SRI put it in a presentation to NAPFI (August 2010), "You can have debris present without damage, but never damage without debris." Likewise, FOD prevention systems work by sensing and detecting not the damage but the actual debris.

Thus FOD is now taken to mean the debris itself, and the resulting damage is referred to as "FOD damage".

Internationally, FOD costs the aviation industry US$13 billion per year in direct plus indirect costs.

The indirect costs are as much as ten times the indirect cost value, representing delays, aircraft changes, incurred fuel costs, unscheduled maintenance, and the like for a total of $13 billion per year[3] and causes expensive, significant damage to aircraft and parts and death and injury to workers, pilots and passengers.

It is estimated that FOD costs major airlines in the United States $26 per flight in aircraft repairs, plus $312 in such additional indirect costs as flight delays, plane changes and fuel inefficiencies.[4]

"There are other costs that are not as easy to calculate but are equally disturbing," according to UK Royal Air Force Wing Commander and FOD researcher Richard Friend.[5] "From accidents such as the Air France Concorde, Flight AF 4590,[6] there is the loss of life, suffering and effect on the families of those who died, the suspicion of malpractice, guilt, and blame that could last for lifetimes.

This harrowing torment is incalculable but should not be forgotten, ever. If everyone kept this in mind, we would remain vigilant and forever prevent foreign object debris from causing a problem. In fact, many factors combine to cause a chain of events that can lead to a failure."

In the United States, the most prominent gathering of FOD experts has been the annual National Aerospace FOD Prevention Conference. It is hosted in a different city each year by National Aerospace FOD Prevention, Inc. (NAFPI), a nonprofit association that focuses on FOD education, awareness and prevention.

Conference information, including presentations from past conferences, is available at the NAFPI Web site.[2] However, NAFPI has come under some critique as being focussed on tool control and manufacturing processes, and other members of the industry have stepped forward to fill the gaps.

BAA hosted the world's first airport-led conference on the subject in November 2010

To find out more about the specifics and examples of FOD and FOD Damage please go here courtesy of

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Article Highlights


FOD Damages to 737 Flying Controls

Original post courtesy of

The Incident
During routine maintenance of a Boeing 737-838, engineers found metal filings next to the stabilizer trim cable drum in the forward electronics and equipment compartment (located underneath the flight deck).

737 Control Schematic (Credit: TAIC)

While investigating further they found what they described as a cleaning ‘rag’ had been trapped in the windings on the forward cable drum.

The Debris (Credit: TAIC)

This foreign object had caused the stainless steel cable to bulge outward, contact the softer aluminium cable guides and the resulting wear had created the metal filings.

Bulged Cables (Credit: TAIC)

In places the cables had worn right through the tubular aluminium spacer and had started to wear through the harder steel bolts that run through the spacers.

able Guide Steel Bolt Damage (Credit: TAIC)

The Investigation
In their investigation report, issued in March 2015, TAIC state, based on lab tests of the material, that it was “highly likely” the debris originated from the Qantas Sydney maintenance hangar. The ‘rag’ was actually a cellulosic or paper-based fibre and polypropylene material, consistent with one of the disposable tear-off paper roll products used at Sydney.

TAIC concluded that:

The integrity of the aeroplane’s stabiliser trim system manual control was compromised. Whilst considered unlikely, there was the potential for the stabiliser trim system manual control to become jammed or at worst disabled if a cable severed.

Another Incident
Interestingly Melbourne and Auckland sites use fabric rags which, due to their greater robustness, have a far greater potential to cause FOD events, such as jamming bell cranks, or jamming landing gear uplocks. The later was demonstrated by a subsequent incident involving a Jetconnect aircraft that had undergone maintenance at the Qantas Melbourne maintenance hangar in September 2013. TAIC did not investigate this incident but do comment on it:

On 11 September 2013 a Jetconnect B737-838, registration ZK-ZQC, was involved in an incident that occurred during a flight to Wellington. The aeroplane had departed from Melbourne, where it had recently had maintenance carried out on the landing gear. After departing Melbourne the flight crew had difficulty raising the right main landing gear. The right main landing gear initially retracted but did not stay up, falling back down once the gear selector was moved to the off position. When the crew reselected the gear lever to the up position, the right main gear retracted and stayed up. After the aeroplane landed at Wellington the ground engineers inspected the landing gear and found a rag wrapped around the right main landing gear uplock assembly.

Qantas… conducted a safety investigation into the second incident, which found that the rag had been used by an engineer to protect against an accidental head strike on the uplock during a maintenance task in the right main wheel well area. The rag was subsequently left on the uplock assembly after the maintenance task was completed, and it interfered with the retraction of the right main landing gear during the next flight.

Safety Lessons
TAIC make no recommendations but state, fairly self-evidently that the key lesson is that:

… all personnel must take care not to leave anything behind inside an aircraft after completing maintenance or cleaning tasks, especially in areas or near systems critical to flight safety.

This incident does demonstrate that in addition to control of tools other items, such small components, reels of lock wire and consumables, also need to be controlled. One such case involved a bearing element from a roller bearing that jammed a Power Control Unit (PCU) on a Turkish B737-400 in 2009.

The landing gear incident, which is unlikely to have happened with paper based wipe, illustrates the downside of fabric cloth / rags.

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