Standard 625 Appendix G: Inspection after Abnormal Occurrences - Canadian Aviation Regulations (CARs)

Content last revised: 2007/12/30

(1) Pursuant to Section 571.02, in the Canadian Aviation Regulations all maintenance shall be performed using the methods, techniques, practices, parts, materials, tools, equipment, and test apparatus specified by the manufacturer of the aeronautical product.

Information note:

This appendix details the requirements for the inspection of aircraft after abnormal occurrences and gives general advice on the performance of such inspections.

(2) Aircraft are approved to operate within certain limits which are considered to constitute normal operation. If these limits are exceeded due to abnormal occurrences, or if the aircraft is exposed to some hazard or stress which was not catered for in the original design, the integrity of the structure or the performance of the powerplant(s) or systems could be impaired. Any report or evidence which indicates that approved limits have been exceeded, or that the aircraft may have sustained damage, shall necessitate an inspection to ensure that the aircraft is still airworthy. The following sections outline in general terms the inspections required after some of the more common occurrences. The procedures described are intended to supplement manufacturer's recommendations, or to cater for those instances where the manufacturer has not provided any detailed instructions. In case of any conflict, the manufacturer's instructions shall prevail. The procedures described are not intended to be complete, or to cover all circumstances. It is the responsibility of the person performing the inspection to assess the circumstances of each case and decide on the appropriate course of action. In doubtful cases, the nearest Transport Canada regional or district office can be consulted.

(3) The inspections detailed in this appendix shall usually be performed by a person who may sign a maintenance release in accordance with section 571.11 of the CARs. In some cases, the nature of the work will be such that the involvement of an AME will be mandatory. This would be the case, for example, where some degree of disassembly was required. It is not possible, however, to state that a person specified in section 571.11 of the CARs is required in all cases. Often, at the time of the occurrence, only the pilot of the aircraft is able to assess the severity of the incident or is available to decide the course of action. Some manufacturers recognize this by allowing for the inspection to be performed in two stages. To cater for situations where no person specified in section 571.11 of the CARs is available, the following procedure is recommended.
(amended 2007/12/30)

(4) Following any abnormal occurrence, including but not limited to those described in this appendix, an entry shall be made in the journey log describing the event. Where possible, the entry shall include some indication of the relative severity of the incident. Prior to the next flight, the aircraft shall be inspected, preferably by a person who may sign a maintenance release in accordance with section 571.11 of the CARs. If no such person is available, the inspection can be conducted by the captain of the aircraft. In this case, the inspection will of necessity be limited to those items which do not require a maintenance release (i.e. does not involve disassembly).
(amended 2007/12/30)

(5) If in the opinion of the captain, the condition of the aircraft is satisfactory for the intended flight, albeit without passengers, he/she shall make an entry in the log to that effect calling for a full inspection by a person who may sign a maintenance release in accordance with section 571.11 of the CARs when available. The captain can then proceed, at his/her discretion, on the intended flight(s) until such time as the aircraft reaches a base where the required additional inspection can be performed. No special flight authority is required under these circumstances. At the first opportunity, the aircraft shall be inspected and a maintenance release shall be issued by a person who may do so in accordance with section 571.11 of the CARs.
(amended 2007/12/30)

(6) If in the opinion of the captain, the aircraft is unairworthy, or if the severity of the incident was such that even after a satisfactory preliminary inspection its airworthiness is in doubt, then the aircraft shall be inspected by a person specified in section 571.11 of the CARs, and a maintenance release signed, before further flight.
(amended 2007/12/30)

(7) In the following sections, no attempt is made to differentiate between those actions which may be part of a pilot’s preliminary inspection, and those which must be performed by a person who may sign a maintenance release in accordance with section 571.11 of the CARs. This distinction will vary according to the type of aircraft and the severity of the incident, and will be primarily governed by the need for a maintenance release. Where there is any doubt regarding the airworthiness of the aircraft, certification by a person who may sign a maintenance release in accordance with section 571.11 of the CARs shall be required prior to flight.
(amended 2007/12/30)

(8) Heavy or Overweight Landings

An aircraft landing gear is designed to withstand landings at a particular aircraft weight and vertical descent velocity. If either of these parameters is exceeded during a landing, it is then probable that some damage can be caused to the landing gear or its supporting structure. Overstressing can also be caused by landing with drift or landing in an abnormal attitude (e.g. nose or tail wheel striking the runway before the main wheels).

Some aircraft have structural elements which are known to give a visual indication that specified "g" forces have been exceeded, but in all cases of suspected heavy landings, the flight crew shall be consulted for details of aircraft weight, fuel distribution, landing conditions and whether any noises indicative of structural failure were heard.

The damage resulting from a heavy landing is normally concentrated around the landing gear, its supporting structure in the wings or fuselage, the wing and stabilizer attachments and the engine mounts. Secondary damage can be found on the fuselage upper and lower skin and structure, and wing skin and structure, depending on the configuration and loading of the aircraft. On some aircraft the manufacturer can recommend that if no damage is found in the primary areas, the secondary areas need not be inspected; but if damage is found in the primary areas, then the inspection shall be continued.

Because of the number of factors involved, it is not possible to lay down precise details of the inspections which must be made after any incident, on any type of aircraft, but a preliminary inspection shall normally include the items detailed below.

  • (a) Landing Gear

    • (i) Examine tires for creep, flats, bulges, cuts, pressure loss and enlargement.

    • (ii) Examine wheels and brakes for fluid leaks, cracks and other damage.

    • (iii) Examine axles, struts and stays for distortion and other damage.

    • (iv) Check shock struts for fluid leaks, scoring and abnormal extension.

    • (v) Examine landing gear attachments for cracks, other damage and signs of movement. In some instances this can require the removal of certain bolts in critical locations, for detailed nondestructive testing.

    • (vi) Examine the structure in the vicinity of the landing gear attachments for signs of cracks, distortion, movement of rivets or bolts and fluid leakage.

    • (vii) Examine doors and fairings for damage and distortion.

    • (viii) Jack the aircraft and carry out retraction and nose-wheel steering tests; check for correct operation of locks and warning lights, clearances in wheel bays, fit of doors and signs of fluid leaks.

  • (b) Wings

    • (i) Examine the upper and lower skin surfaces for signs of wrinkling, pulled rivets, cracks and movement at skin joints. Inertia loading on the wing will normally result in wrinkles on the lower surface and cracks or rivet damage on the upper surface, but stress induced by wing-mounted engines can result in wrinkles on either surface.

    • (ii) Check for signs of fuel leaks and seepage from integral tanks.

    • (iii) Examine wing root fillets for cracks and signs of movement.

    • (iv) Check flying controls for freedom of movement.

    • (v) Check balance weights, powered flying control unit mountings and control surface hinges for cracks, and control surfaces for cracks or bucking.

    • (vi) Check spars for distortion and cracks.

  • (c) Fuselage

    • (i) Examine fuselage skin for wrinkling or other damage particularly at skin joints and adjacent to wing and landing gear attachments.

    • (ii) Examine pressure bulkheads for distortion and cracks.

    • (iii) Examine the supporting structure of heavy components such as galley modules, batteries, water tanks, fire extinguishers, auxiliary power units, etc. for distortion and cracks.

    • (iv) Check that the inertia switches for fire extinguishers, emergency lights, etc, have not tripped.

    • (v) Check instruments and instrument panels for damage and security.

    • (vi) Check ducts and system pipelines for leaks and buckling.

    • (vii) Check fit of access doors, emergency exits, etc., and surrounding areas for distortion and cracks.

    • (viii) Check loading and unloading operation of cargo containers and condition of cargo restraint system.

  • (d) Engines

    • (i) Check engine and propeller controls for full and free movement.

    • (ii) Examine engine mounts and pylons for damage and distortion, tubular members for bowing and cracks at welds, mounting bolts and attachments for damage and evidence of movement.

    • (iii) Check freedom of rotating assemblies - on piston engines, check freedom of rotation with spark plugs removed.

    • (iv) Examine engine cowlings for wrinkling and distortion, and integrity of fasteners.

    • (v) Check for oil, fuel and hydraulic fluid leaks.

    • (vi) Check propeller shaft for alignment.

  • (e) Empennage

    • (i) Check flying controls for freedom of movement.

    • (ii) Examine rudder and elevator hinges for cracks, and control surfaces for cracks and distortion, particularly near balance weight fittings.

    • (iii) Examine stabilizer attachments and fairings, screw jacks and mountings for distortion and signs of movement.

  • (f) Engine Runs

    Provided that no major structural distortion has been found, engine runs shall be carried out to establish the satisfactory operation of all systems and controls. A general check for system leaks shall be carried out while the engines are running, and on turbine engines the rundown time shall be checked.

  • (g) Helicopters

    The inspections necessary on helicopters are broadly similar to those detailed in the preceding paragraphs, but additional checks are normally specified for the main rotor blades, head and shaft, tail rotor and transmission. The inspections outlined below are typical.

    • (i) Examine the rear fuselage or tail boom for evidence of strike damage from the main rotor blades, and if damage is found, check for cracks, security, and symmetry.

    • (ii) Remove the main rotor blades and examine them for twisting and distortion. Check the surface for cracks, wrinkles or other damage, and check the security of the skin attachment rivets or structural bonding. If the main rotor blades are badly damaged through impact with the tail boom or ground, certain components in the transmission can be shockloaded, and it shall be necessary to refer to the instructions for rotor strikes (see section13 below).

    • (iii) For the main rotor head, disconnect pitch change rods and dampers, and check that the flapping hinges, drag hinges and blade sleeves move freely, without signs of binding or roughness. Examine the rotor head and blade stops for cracks or other damage, and the dampers for signs of fluid leaks. Damage in this area can be an indication of further damage inside the main gearbox.

    • (iv) Examine the tail rotor blades for damage and security, and the coning stops for evidence of damage. Damage to the tail rotor blades which is beyond limits shall entail either further inspection, or replacement of the hub, pitch change links, tail rotor gear box and drive shaft.

(9) Flight in Severe Turbulence

The type of damage that results from flight through severe turbulence is similar to that resulting from a heavy landing, the major difference being that the damage is less localized, and that wheel and brake assemblies are unlikely to be affected.

On some aircraft an indication of the severity of the loads experienced can be obtained from accelerometers or fatigue meters. These instruments, however, are designed to record steady loads, and peak forces recorded during flight through turbulence can be exaggerated due to instrument inertia. Generally, readings outside the range of -.5 g to + 2.5 g on transport category aircraft are cause for investigation. Most aircraft do not have such instrumentation, and all incidents of flight through severe turbulence shall be investigated.
(amended 2007/12/30)

Severe turbulence can cause excessive vertical or lateral forces on the aircraft structure, and the effects can be increased by the inertia of heavy components such as engines, fuel tanks, water tanks and cargo. Damage can be expected at main assembly points such as the wing to fuselage joints, tail to fuselage joints and engine mountings. Damage can also occur in those areas of the wings, fuselage, stabilizer and control surfaces where the greatest bending moment takes place (i.e. part way along their length, and can be indicated by skin wrinkles, pulled rivets or similar faults).

An inspection for damage after a report of flight through severe turbulence shall include the inspections detailed in Section (8) above, except, in most cases, those covering the landing gear.

Information note:

Further dismantling and, in some cases, removal of some portions of the skin can be necessary in order to inspect supporting structure where skin damage has been found.

(10) Exceeding of Airspeed/Acceleration Limits

Where it is reported that an aircraft has exceeded its approved airspeed or acceleration limits, the inspection required is the same as that required following flight through severe turbulence.

Where the limit exceeded was that applicable to a particular configuration (e.g. gear or flap extension limits), or where the report relates to failure to observe loading or wing bending relief limits (e.g. application of excessive loads prior to depletion of centre wing tanks), then the subsequent investigation can be limited to the affected areas of the structure.

(11) Burst Tire Incidents

If a tire bursts during taxiing, take-off or landing, fragments of the tire can cause damage to parts of the aircraft in line with the wheel disc. Damage can also occur due to the wheel rolling on the paved runway and transmitting shocks to the landing gear leg and supporting structure.

Multiple wheel landing gears will generally be less seriously affected by a single burst tire, but the axles, bogies, torque links or steering mechanism can become bowed or strained as a result of the effects of uneven loading. In most cases, the wheel on which the burst occurred shall require repair or removal from service.

In addition, the following inspections shall be carried out:

  • (a) Examine the wheels and tires which have not burst.

    Information note:

    Where one of the tires on a multiwheel undercarriage has burst, it can be specified by the aircraft manufacturer that all tires on that leg or axle shall be discarded, or removed for detailed examination.

  • (b) Examine the brake units on the affected leg for damage. On those wheels which are not fitted with fusible plugs, the tire burst can have resulted from overheating caused by a binding brake, and when the replacement wheel is fitted, attention shall be given to the operation of the associated brake including, in particular, freedom of rotation of the wheel with brake released.

  • (c) Examine the landing gear bay for damage and hydraulic fluid leaks.

  • (d) Examine the affected leg, including pipelines, operating jacks, etc., for damage and hydraulic fluid leaks.

  • (e) Inspect the supporting structure and attachments of the affected leg for cracks, warped panels and loose rivets. In some instances it can be specified that certain highly stressed bolts in the supporting structure or retraction mechanism shall be removed for nondestructive testing.

  • (f) Examine the adjacent fuselage or wing skins and landing gear doors for damage.

  • (g) Check engines for possible ingestion of debris.

(12) Immersion in Water

The following requirements are based on immersion in non-contaminated water. It is the responsibility of the person specified in section 571.11 of the CARs performing the inspection to determine if any contaminating elements exist, and extend the scope of the inspection as necessary. Examples of contaminants which may have to be taken into consideration include alkali, sulphur, salt, etc. Other important considerations are the length of time the aircraft has been submerged, especially if contaminants exist, and the temperature of the water. If temperatures are below freezing, tubing in the fuselage structure is liable to have been distorted or split through the formation of ice.
(amended 2007/12/30)

The general inspection requirements for aircraft which have been immersed in water are listed below. To them shall be added any additional requirements specified by the manufacturer, and additional inspections for any damage incurred during the entry into the water or during the recovery operation. The inspections listed below are considered the absolute minimum required following short term immersion in uncontaminated water. If the aircraft has been immersed for a period in excess of 30 days (or 24 hrs. in the case of salt water), additional inspections shall be necessary.

  • (a) Aircraft Structure

    • (i) Examine all structure for damage (i.e. skin wrinkles, warping, bulges or splits in tubular structures).

    • (ii) Remove or open all inspection panels to allow complete draining and drying. Cabin lining, flooring and side panels shall be opened sufficiently to allow drying and inspection. On fabric covered components, cut sufficient circular holes to allow draining, drying and inspection of the structure. Special attention shall be paid to glued joints on wooden structures.

    • (iii) Check tubular structure for trapped water. Examine tape wrappings on tubular frames for thorough drying.

    • (iv) Lubricate with grease where fittings are provided, and all other moving parts with light engine oil.

    • (v) Drain fuel tanks and lines and flush tanks with a suitable rapidly evaporating solvent.

      Information note:

      Maintenance personnel should ensure that the solvents used for flushing have no detrimental effect on the flexible hose construction material.

  • (b) Instruments

    • (i) Remove all instruments, open sufficiently to allow drying. Lubricate and test. All primary flight instruments shall be forwarded to an approved overhaul organization for recertification.

    • (ii) Disconnect all lines and drain thoroughly, paying particular attention to low spots where water can be trapped.

  • (c) Electrical and Avionics Equipment

    • (i) Loosen all wire bundles and shielded cables sufficiently to allow complete drying.

    • (ii) Check all connections and remove corrosion.

    • (iii) Clean switches (open type), solenoids, reverse current relays and voltage regulators (except carbon pile type) with a suitable rapidly evaporating solvent. Carbon pile type voltage regulators shall be returned to an approved overhaul facility.

    • (iv) Replace toggle switches and circuit breakers.

    • (v) Clean and test all radio units and accessories.

  • (d) Engines (if immersed while cold)

    • (i) Examine engine and propeller for damage. Bent propeller blades shall necessitate the examination of the engine for propeller strike damage.

    • (ii) Drain oil from sumps, oil cooler and tank.

    • (iii) Drain water from cylinders by rotating crankshaft, with spark plugs removed and lower intake pipes loosened.

    • (iv) Drain carburettor, flush with fuel or alcohol, and then flush with very light oil. Injection type carburettors shall be forwarded to an overhaul agency for dismantling, inspection and testing.

    • (v) Remove magnetos, drain, oven dry, relubricate and reinstall.

    • (vi) Remove all accessories, drain, dry, relubricate and reinstall.

    • (vii) Clean spark plugs and ignition harness, dry and test.

    • (viii) Drain and replenish oil tank with oil of the correct grade.

    • (ix) Start engines, if oil pressure is normal, continue running until operating temperatures are obtained (cylinder head and oil).

    • (x) Stop engines and check oil screens.

    • (xi) Carry out complete power run and ensure that all applicable specifications are met, and that all accessories are operating normally.

  • (e) Additional Checks if Engine Immersed while Hot

    • (i) Piston Engines

      Due to the thermal shock encountered with the sudden cooling of the cylinder assemblies, all cylinders shall be removed and dismantled; cylinders, cylinder heads, pistons, valves, valve seats and valve springs shall be inspected for distortion and cracks.

    • (ii) Turbine Engines

      Turbine engines shall be completely dismantled for internal inspection by an approved turbine engine overhaul organization.

  • (f) Additional Checks if Engine Immersed while Running

    • (i) Piston Engines

      Due to the danger of forming a hydraulic lock which can result from the entry of water into the cylinders, the engine shall be completely dismantled for internal inspection by an approved overhaul organization.

    • (ii) Turbine Engines

      Turbine engines shall be completely dismantled for internal inspection by an approved overhaul organization.

  • (g) Propellers

    Cleaned and re-lubricated. Propellers with control domes or cylinders which are removable in the field shall be opened and checked internally.

(13) Propeller and Rotor Strikes

Engines and transmission systems which have been shockloaded as a result of the propeller or rotor striking the ground or some object while the engine is running shall be inspected in accordance with the following paragraphs:

  • (a) A preliminary inspection shall be made of the blade itself and, if possible, of the object which was struck to aid in estimating the level of shock which can have been transmitted. It is not expected that an accurate assessment be made, but rather that the inspector shall form a general impression of whether the impact was severe or mild. If the level of impact is in doubt, it shall be assumed that a severe shock has been transmitted. In addition to a visual examination, the propeller or rotor shall be checked for correct tracking. Out of track limits shall be found in the appropriate maintenance manual but, as a general guide, a propeller which is out of track by more than 0.125 inch (3,18 mm.) is cause for further investigation. A visual inspection of the reduction gear case for oil leaks or cracks shall also be carried out.

  • (b) The need for further investigation will depend upon the results of the preliminary examination, and on the assessment by a person specified in section 571.11 of the CARs of the probability of further damage, based on the nature of the incident. If further investigation is indicated, the propeller shaft or flange shall be checked for eccentricity (run out check). Limits are those specified by the manufacturer. If the propeller shaft or flange is out of limits, an internal inspection shall be required. In the case of a geared piston engine this shall entail removal of the reduction gear for a check of the crankshaft run out. With a direct drive engine the crankcase shall have to be opened and checked for distortion, cracks or other damage. This check shall include the crankshaft damper assemblies. If the impact was severe, consideration shall also be given to the possibility of structural damage due to loads being transmitted through the engine mounts.
    (amended 2007/12/30)

  • (c) In the case of helicopters, the following additional checks shall be made:

    • (i) Remove the main rotor blades and examine them for twisting and distortion. Check the surface for cracks, wrinkles or other damage, and check the security of the skin attachment rivets or structural bonding. If the main rotor blades are badly damaged through impact with the tail boom or ground, check the main rotor shaft, pitch change rods and main gear box mounting bolts for cracks and distortion.

    • (ii) For the main rotor head, disconnect pitch change rods and dampers, and check that the flapping hinges, drag hinges and blade sleeves move freely without signs of binding or roughness. Examine the rotor head and blade stops for cracks or other damage, and the dampers for signs of fluid leaks. Damage in this area can be an indication of further damage inside the main gearbox.

    • (iii) Examine the tail rotor blades for damage and security, and coning stops for evidence of damage. Damage to the tail rotor blades which is beyond limits shall normally entail either inspection or replacement of the hub, pitch change links, tail rotor gear box and drive shaft.

    • (iv) Examine tail rotor drive shafts, universal joints, bearings and support structure for cracks and distortion. Check for freedom of rotation.

(14) Lightning Strikes

  • (a) Lightning strikes usually cause damage at two points on an aircraft: strike damage where the discharge enters the aircraft; and static discharge damage subsequent to the strike.

    Strike damage is generally found at the wing tips, propellers, leading edges of wings and tail unit, and at the fuselage nose, but on some aircraft types other areas can be particularly susceptible, and this information shall be obtained from the appropriate maintenance manual. Static discharge damage can usually be found at wing tips, trailing edges and antennae.

    Information note:

    Strike damage is usually in the form of small circular holes in the exterior skin, either in clusters or spread out over a wide area, and often accompanied by burning or discolouration, blisters on radomes and cracks in glass fibre. Static discharge damage is usually in the form of local pitting and burning at trailing edges.

  • (b) Since both lightning and turbulence occur in thunderstorms, an inspection for lightning damage shall often coincide with an inspection following reported flight through severe turbulence. The areas mentioned in subsection (a) above shall be examined for signs of strike or static discharge damage, and bonding strips and static discharge wicks shall be examined for burning and disintegration. All control surfaces, including flaps, spoilers and tabs, shall be inspected for damage at their hinge bearings; unsatisfactory bonding can have allowed static discharge and tracking across the bearings, causing burning, break up or seizure. A check for roughness and resistance to movement at each bearing will usually indicate damage at such points. In addition, the following inspections shall be carried out:

    • (i) Examine engine cowlings and engines for signs of burning or pitting.If a lightning strike is evident, tracking through the bearings can have occurred, and some manufacturers recommend that the oil filters and chip detectors should be examined for signs of contamination; this check shall be repeated periodically for a specified number of running hours after the occurrence;

    • (ii) Examine the fuselage skin and rivets generally for burning or pitting;

    • (iii) If the landing gear was extended when the lightning strike occurred, examine the lower parts of the gear for static discharge damage. Check for residual magnetism and demagnetize where necessary;

    • (iv) Functionally check the radio and radar equipment, instruments, electrical circuits and flying controls in accordance with the relevant chapters of the maintenance manual. On some aircraft, a bonding resistance check on radomes can also be specified; and,

    • (v) Carry out a compass swing.

(15) High Winds or Jet Blast

Considerable damage can be caused to parked aircraft by high winds or by jet blast/prop wash from other aircraft taxiing or running up in the vicinity. Small aircraft are particularly vulnerable to this type of damage, which can be caused by the blast itself or by debris blown into the aircraft. Following such incidents, the aircraft shall be inspected as follows:

  • (a) Inspect flying control surfaces for distortion and loose rivets or other signs of internal damage. If the surfaces were unlocked at the time of the incident the control stops, stop cables and surrounding structure should also be checked;

  • (b) Inspect the structure generally, including windows, for impact damage such as chips and dents, and examine the air intakes of engines, heat exchangers, cooling ducts, etc. for debris;

  • (c) In the case of small aircraft, and particularly where the blast has been strong enough to move the entire aircraft, consideration shall be given to the need for an internal inspection for damaged structural elements and/or a symmetry check of the complete aircraft.

(16) Spillage of Corrosive Substances

The action taken following spillage of a corrosive substance shall depend upon many factors, including the nature of the substance, the location of the spill and the time elapsed between the occurrence and its discovery. In general, the procedure consists of:

  • (a) Removal of the Spilt Substance

    This shall preferably be done by draining at the nearest drain hole but, if this is not possible, a vacuum cleaner can be used, or the spill mopped up with rags. In the case of mercury, the use of a velvet cloth can help to prevent "beading". The use of blowing hoses to disperse corrosive deposits is not recommended, as this will tend to distribute the substance over a wider area. Care shall be taken to avoid contact with the substance (use masks, gloves, goggles, etc.);

  • (b) Neutralizing the Residue

    Acid spills can be neutralized with a bicarbonate of soda solution. Alkaline spills can be neutralised with a boric acid solution. Chlorine can be treated with water to which acetic acid (vinegar) has been added. Litmus paper will indicate when a neutral ph level has been achieved. Mercury spills can be treated by sprinkling calcium sulphide on the affected area, while phosphates, nitrates and carbonates can be treated by the application of bleach or a strong soap solution;

  • (c) The entire area shall be rinsed with copious amounts of clean water;

  • (d) Access panels shall be removed, and the aircraft positioned to ensure a flow of fresh air through the affected area;

  • (e) Radiographic inspection can be required to detect small particles of mercury, or corrosion pits out of the direct line of sight; and

  • (f) Re-protect the area by painting, lubrication, etc, as applicable.

    Information note:

    Depending on the nature of the spill, and the amount of damage caused, it may be necessary to schedule additional follow-up inspections of the area until it can be determined that no danger of further corrosion exists.

(17) Overspeed-overtemp-overtorque Incidents

Manufacturers' manuals usually contain detailed instructions on the procedures to be followed after this type of incident. If no instructions are available, the manufacturer shall be contacted and provided with full details of the incident. Collateral information can be of importance (e.g. in the case of a turbine engine overtemp, the RPM at which the overtemp occurred is usually an important factor).

(18) Misfuelling

The term misfuelling can include filling with contaminated fuel or with fuel of an incorrect grade. The latter is sometimes difficult to detect, as the incorrect fuel can mix with the fuel already in the tanks, and appear identical to the naked eye. The most common error (and one of the most dangerous) is fuelling piston engined aircraft with jet fuel. Sophisticated analysis techniques are available to detect contamination of this kind, but one method of detection which is readily available in the field is the "kraft paper" test.

This consists of allowing a drop of the suspected fuel to fall on to a sheet of plain brown paper of the type used for grocery bags, and observing the results. Uncontaminated gasoline will evaporate within 1 to 5 minutes (depending on the temperature), leaving an irregularly shaped stain. Fuel containing as little as 2% kerosene can take 15 minutes or longer to evaporate, and will leave a circular stain.

If an aircraft has been refuelled with contaminated fuel, or with the wrong grade of fuel, the action taken will depend primarily upon whether the engine(s) have been operated on the fuel in question. If the misfuelling is detected before the engines have been run, it is merely necessary to ensure that the fuel is drained.

The aircraft (or the affected tanks) shall be completely defuelled, and the tanks drained at the lowest point. With tail wheel equipped aircraft this can entail placing the aircraft in the flying attitude to ensure that no residue of contaminated fuel remains in the lowest part of the tanks. After draining and replenishing with the correct grade of fuel, the engine supply lines shall be flushed, and an engine ground run carried out.

If the engines have been run on the contaminated fuel, the action taken will depend on the type of engine and the nature of the contamination. Turbine engines are generally more tolerant of misfuelling than piston engines, and some turbine engine manufacturers specify that their engines can be run for a certain period of time on aviation gasoline. Reference shall be made to the maintenance manual and the engine type certificate data sheet for details.

Piston engines which have been operated on unapproved fuels can have experienced detonation and shall be inspected for damage which could result. The inspection shall commence with an examination of the spark plugs, valves and valve seats, and the piston crowns. If any damage is detected the engine shall be dismantled completely for internal examination.

(19) Exposure to Volcanic Ash

Volcanic eruptions are rare, but when they do occur the ashes which are ejected can spread over a wide area and can potentially affect a great number of aircraft. Volcanic ash is highly abrasive, and can be acidic. If the particles are ingested by a running engine, they will melt when exposed to combustion chamber temperatures and form a glass-like ceramic coating on internal engine parts.

A number of manufacturers have provided instruction for the treatment of aircraft which have been exposed to volcanic ash, and these instructions shall be followed. In general, they consist of the removal of debris by vacuum cleaner (avoid the use of water, which can combine with the ash to form a cement like substance, and can exacerbate the corrosive effects). Care shall be taken to avoid the scratching of polished surfaces, such as transparencies or the exposed pistons of hydraulic actuators. Air filters shall be changed, and system which are open to the atmosphere (pitot static systems, pressure sensing vents, etc.) checked. If the engines were running at the time of the exposure, borescope checks of the internal components shall also be required.

(20) Ingestion of Dry Chemical Extinguishant

Dry chemical extinguishant, if ingested into a running piston engine, can be deposited on the inlet valve stems in the form of a sticky, shellac-like substance. This deposit can cause sticking of the valves and subsequent damage to the engine.

Whenever dry chemical extinguishers are used on an aircraft engine, the induction system and surrounding area shall be thoroughly cleaned prior to engine starting. If any signs of ingestion of powder into the engine are found, the valve stems shall be inspected for deposits, and if necessary, a top overhaul carried out.

(21) Bird Strikes


(22) Ground Collisions


(23) Other Occurrences

Occurrences not covered in the preceding sections, or peculiar to a particular aircraft type, can also necessitate special inspections, and these are usually specified in the appropriate maintenance manual. Where no specific instructions exist, experience on the type of aircraft, combined with a knowledge of the structure and systems, will normally enable a satisfactory inspection to be carried out.

Information note:

In cases of doubt, the aircraft manufacturer and/or the local Transport Canada airworthiness office can be consulted.