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Foreign Object Damage II
On the following article, you will get to know a little bit more about FOD's and will also have tips on how to avoid them during the operation of an aircraft. On this issue, we bring out the continuation of the article 'Foreign Object Damage', started on the last issue of the ATT Technical Bulletin. On the previous issue, we showed how above-any-suspicion objects could do damage to the aircraft engine. Now, we will show how foreign objects could also damage other systems or components of the aircraft and that, as well as in the cases when the engine is affected, they can be responsible for aeronautical accidents. Damage to the tires. This is such a usual occurrence that, at most times, little attention is paid to it. However, this problem is coated by the two features that stimulate the prevention activity: high cost and high danger potential. For a mid size air taxi company or airline, the cost due to the loss of tires because they do not present the minimum conditions for the retreading process could get to hundreds of thousand dollars per year. The risk of losing control of the aircraft while landing due to FOD does exist and should not be disconsidered. Evidently, the risk associated to the occurrence of FOD to the wheels is not restricted just to the tires. There are, for example, registers of objects that have damaged the brake systems, affecting the disk and even the hydraulical tubing. Contamination Another extremely common occurrence of FOD, yet not less dangerous, is the contamination of systems due to foreign objects or even products (gases and liquids) in that environment. Some common examples are the contamination of fuel by water, the contamination of oil by metallic parts and even the contamination of oxygen by other gases or by fungus. All of them have a very high potential for the occurrence of an accident. Collision with birds They are very common and important, especially in Brazil, when we consider the size and the weight of the most commonly involved birds in the episodes of flight collision: the buzzard can be up to 2.5 kg heavy. The problem is that the key here is the product mass x speed that, due to the aircraft speed, turns the bird into something similar to an artillery missile. Interference of objects that are free in the cabin Thats right! Objects that are free in the cabin, such as a mere pen or field book frame, could be characterized as FOD. As examples, we can mention the occurrence of a pilot who lost command of the aircraft because of a field book frame that had fallen on the control stick basis, or the episode of loss of the soil direction control due to the interference of an electrical box that had been forgotten by the maintenance team on the floor, behind the pedals. In both cases, the simplicity of the fact does not reduce the potential risk of its consequences. Interference of Objects in other systems The maintenance services can turn into potential sources of FOD to the aircrafts of their own organization when done displicently and without supervision. A case that has become famous, for example, is the one presented in a film, in which a pair of pliers had been forgotten by the mechanic at the air entry of an aircraft just before a flight and it caused the breakdown of the plane. There are cases of lower cost, but not of lower risk potential, in which the tool was forgotten inside the aircraft structure (wing) and provoked the blockage of the aileron command cables. The possibilities are widely diverse. Prevention The FOD prevention work depends in great part on the maintenance, inspection and cleaning of the aircraft and environment that surrounds it. Nonetheless, there are some actions in the operation of the aircraft that can be decisive to avoid FOD. During the operation of the aircraft on the soil, the use of more elevated potencies must be avoided with the intention to prevent the blowing of sweepings into the operational area or into the air entry of other aircrafts. While taxiing, cut-offs must be avoided in the curves, with a view to helping the engines from passing by the non-paved areas. This contributes to the prevention of FODs for both, the aircraft that is taxiing and the ones that will follow it. Special attention should be paid to the aircrafts with high wingspan and with engines that are apart from the fuselage because in most cases, even if the taxiing is performed within the guiding line, it may be possible that the external engines are not on the lane. The worry in relation to the blowing of the operating aircraft must be present in the delimitation of the parking slots (detachment of the boxes) and in the marking of the taxi bands on the floor. Taxiing must be avoided too close to the preceding aircraft. Taxiing with open canopy is a procedure that must always be avoided when exposed to the risks of objects especially letters being blown out and ingested by the engines. In case it is really necessary to do it, it must be certified that these objects are fixed inside the cabin. Formation take-offs are a situation of high risk of FOD for the back aircrafts maximum attention is always recommended. The use of air entry protectors in the engines of the parked aircrafts, both in courtyards and hangars, in headquarters or not, is essential to reduce the risk of foreign object damage (blown sweepings, rain accumulation, presence of small animals, etc.). On the other hand, the inspection previous to flight or even the external inspection cannot be neglected, or else, there could be the risk of turning the installed protector into the ingested object. Source: Adapted from the Cenipas booklet. Collaboration: Commander Rui Mota Issued on the Technical Bulletin of the Association of TAMs Crew Members (ATT)

Criado em 18/07/2005.
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