CAA NZ AME Subject 2: Aircraft Engineering Knowledge common mistakes
CAA NZ AME Subject 2: Aircraft Engineering Knowledge · Understand the traps and how to avoid them.
When asked whether a wing must withstand ultimate load without permanent deformation, the candidate answers yes and applies the 1.5 factor to the wrong condition.
Limit load and ultimate load are studied together, so the 1.5 factor gets attached to deformation instead of failure.
What to do instead
Memorise the pair: limit load is the maximum expected in service and must cause no detrimental permanent deformation; ultimate load is 1.5 x limit and the structure must not fail for at least 3 seconds. Check each exam statement against deformation versus failure.
Calculates the load factor in a 60-degree level bank as cos 60 = 0.5 or about 1.15 instead of 2.0.
Confuses the horizontal component of lift with total lift, so cosine is used where the reciprocal is required.
What to do instead
Use n = 1/cos(bank angle). Memorise 30 degrees = 1.15, 45 degrees = 1.41, 60 degrees = 2.0. Cross-check that stall speed rises by the square root of n, so at 60 degrees it is about 1.41 times the level-flight stall speed.
States that hydraulic system pressure rises whenever the engine-driven pump speed increases, and that the relief valve sets normal operating pressure.
Carries over automotive thinking and does not distinguish fixed-displacement pumps from pressure-compensated variable-displacement pumps.
What to do instead
Identify the pump type first. In a fixed-displacement system the relief valve limits maximum pressure and bypasses excess flow; pressure does not keep rising with RPM once it opens. In a pressure-compensated pump, displacement varies to hold pressure and the relief valve is a backup.
Labels pneumatic boots on a wing leading edge as anti-ice and says they stop ice from forming.
The terms sound interchangeable, but boots operate cyclically after ice has already accreted.
What to do instead
Classify by timing: anti-ice prevents formation (thermal, chemical, electrical); de-ice removes accumulated ice (boots). For boots, state the cycle: inflate to crack ice, deflate, repeat; never leave them inflated.
Defines detonation as the fuel-air mixture igniting before the spark plug fires.
Both detonation and pre-ignition are abnormal combustion events with high cylinder head temperature, so the definitions blur under exam pressure.
What to do instead
Build a cause-and-effect table. Pre-ignition is ignition before the spark, often from a hot spot such as a glowing plug or carbon deposit. Detonation is spontaneous secondary combustion after normal spark ignition, causing a rapid pressure rise.
Uses the exhaust gas temperature limit as if it were the turbine inlet temperature limit, or says EGT probes measure gas before the first turbine stage.
EGT and TIT are both turbine-engine temperature limits, but the probe locations and limiting values differ.
What to do instead
Draw the engine station numbers. TIT is at the turbine inlet and is often not measured directly; EGT is measured between turbine stages or in the exhaust. Never interchange the limits; use the manufacturer's published values for the specific engine.
Says a blocked static source makes the airspeed indicator read high during a climb.
The candidate reasons from trapped pressure but reverses the relationship between the airspeed indicator and the altimeter.
What to do instead
Memorise the blocked-system behaviour. Blocked pitot: the ASI behaves like an altimeter, reading high in a climb. Blocked static: the ASI reads low in a climb and high in a descent, the altimeter freezes, and the VSI reads zero.
Confuses electrical bonding with grounding and describes measuring bonding resistance with an ordinary ohmmeter while the bus is live.
Both provide return paths, but bonding is for fault current and static discharge, not an earth return, and live measurement is invalid.
What to do instead
Define bonding as a low-impedance path between metallic parts and grounding as the return to the aircraft structure. De-energise and isolate the circuit, use a bonded milli-ohmmeter, and compare the reading with the aircraft maintenance manual limit.
Installs a cadmium-plated steel fastener directly into an aluminium alloy structure and claims the cadmium plating protects both metals.
Cadmium is cathodic to aluminium in the galvanic series, so a direct couple makes the aluminium the anode and promotes corrosion.
What to do instead
Treat cadmium-plated steel in aluminium as a galvanic couple. Use a protective barrier such as primer or sealant, an insulating washer where specified, or a compatible finish. Wet-install with the approved protective compound and inspect for corrosion.
States that a maintenance release is issued by the CAA and replaces the certificate of airworthiness.
Airworthiness documents overlap, so the roles of the regulator, the approved maintenance organisation, and the licensed engineer become blurred.
What to do instead
Separate the documents by purpose and issuer. The certificate of airworthiness is the state airworthiness certification; a maintenance release certifies that specified maintenance has been completed by an authorised person and has limited validity. Learn who issues each, what each certifies, and when each is required.