2.1 Theory of Flight & Major Aircraft Components

Why a cabin crew member studies aerodynamics

The Nigerian syllabus places theory of flight and major aircraft components at the head of knowledge subject 2 for two practical reasons. First, cabin crew are the operator's eyes on the exterior during walk-round and on the wing during flight, and a report is only useful if it names the right part. Second, passengers ask, and a crew member who can explain a wing flexing in turbulence or the noise of flaps retracting removes anxiety that would otherwise become a cabin management problem.

The four forces

In steady, straight and level flight lift equals weight and thrust equals drag. To climb, thrust is increased so that it exceeds drag; to descend, thrust is reduced. An aeroplane does not "point up and go up" indefinitely — climb performance is bought with engine power.

How a wing makes lift, and how it stops

Air flowing over the curved upper surface of a wing is accelerated and its static pressure falls, while air beneath the wing is slowed and its pressure rises. The pressure difference across the aerofoil produces lift. Lift increases with:

• Airspeed — lift varies with the square of speed, so doubling speed quadruples lift;
• Angle of attack — the angle between the wing chord line and the relative airflow;
• Air density — cold, dense air at sea level produces more lift than the hot, thin air of a Nigerian afternoon at an inland aerodrome;
• Wing area and camber — which is why flaps exist.

Beyond the critical angle of attack the airflow separates from the upper surface and lift collapses. This is a stall. The critical angle is a fixed property of the aerofoil, so an aeroplane can stall at any airspeed and any attitude. Cabin crew normally experience the precursors rather than the event: stick shaker, buffeting, and an immediate nose-down and power-up recovery. Recognise it, secure yourself, and do not stand up.

High-lift devices and the noises passengers hear

Landing gear extension and the associated hydraulic noise typically follows flap extension on approach; thrust reversers produce the loud roar immediately after touchdown.

The three axes and the primary controls

A coordinated turn combines roll and a small amount of yaw; passengers feel it as an increase in apparent weight, not as a sideways force.

Major components

• Fuselage — the pressurised tube carrying the flight deck, cabin, cargo compartments and, on most airliners, the wing centre section and fuel tanks. Cabin crew locate defects by fuselage station, door number or seat row.
• Wings — structure, fuel tanks, high-lift devices, flight controls and, on low-wing airliners, main landing gear housing. Wings flex in flight by design; visible movement is normal.
• Empennage — the tail assembly: horizontal stabiliser with elevators, vertical stabiliser with rudder, and on some types an auxiliary power unit (APU) exhaust in the tailcone.
• Powerplant — turbofan engines suspended on pylons under the wing or mounted on the rear fuselage, comprising fan, compressor, combustion chamber, turbine and exhaust, enclosed by cowlings. Cabin crew must be able to identify engine number by convention — number 1 is the leftmost engine viewed from behind, looking forward.
• APU — a small gas turbine, usually in the tailcone, that supplies electrical power and bleed air on the ground and, within limits, in flight.
• Landing gear — nose gear and main gear, with brakes and anti-skid; retracted into bays after take-off.

Reporting like a professional

Cabin crew reports carry weight in the technical log. Compare two reports of the same observation:

• "Something looks wrong on the wing."
• "During climb from Lagos, from seat 22A on the left side, I observed a panel on the wing leading edge, outboard of the engine, standing proud by about a hand's width, with no visible fluid leak."

The second report tells the flight crew which device is affected, which side, which phase and whether fluid is involved. Learn the component names so that the report you make can be acted on.