The root cause of this warpage is over-tightening the front two carburetor mounting bolts, often in combination with a base gasket that lacks hard nylon inserts for the bolt holes.

Among recent subjects of inspection have been cargo door locks, engine mounting bolts and skin rivets and engine blades.

Mounting bolts and screws included.

Federal safety investigators are urging closer inspection of the engine mounting bolts on hundreds of Boeing 737 airplanes to detect possible cracking.

Even later models (by frame number TB1029) were fitted with a further small light steel plate shielding the carburettor float bowl and fitted under the heads of the front two engine mounting bolts.

Thermal cycles and engine vibration tend to loosen the six 10mm upper pan mounting bolts inside the motor.

Fined Peter Rondeau, crew chief for Kenny Wallace, $10,000 for using unapproved spring mounting plates and bolts.

Be especially careful to check the engine mounting bolts, as well as the bolt that holds the cutting blade in place.