An ILS (Instrument Landing System) is defined as a precision runway approach aid based on two radio beams which together provide pilots with both vertical and horizontal guidance during an approach to land.

The ILS aerials transmit two lobes. For a pilot on final, the lobe to his right is modulated at a frequency of 150 Hz and the one to his left at 90 Hz. The point where the lobes meet is the centre line of the runway. As the signals on the lobe move from the centre line to either side, their amplitude increases. This means the magnitude of their depth modulation increases. The depth modulation can be considered as a percentage. For example, if an aircraft receives a 15% depth modulated signal from the left and a 5% depth modulated signal from the right, the difference of modulation becomes 10% to the left. This electrical imbalance is sent to the aircraft and the localizer needle is designed in such a way that it will show a deflection to the opposite direction, telling the pilot to go to the right.

When on the centre line, the modulation difference is zero and the needle centres itself.

The glide slope or the glide path provides the pilot with vertical guidance. The glide slope is set such that a glide slope angle of 3 degrees is maintained by the pilot. The needle of the slope moves up, if the aircraft is too low and moves down if it is too much above the required path. The glide slope is on the UHF band (329.15 - 335 Mhz).

The glide slope operates the same way as the localizer. The only difference is that the lobes are emitted on the vertical plane. The upper lobe is modulated at 90 Hz while the bottom one at 150 Hz. Exactly the same way as before, the needle of the slope moves based on the difference in depth modulation. As like before when the modulation difference is nil, the glide needle moves to the very centre of the instrument.

662 kts

Local speed of sound = 39 x √(Temperature in Kelvin)

15°C in Kelvin is (15 + 273) = 288

So the local speed of sound = 39 x √288 = 662 kts

-15°C

because:

-2°C per 1000 feet gives -30°C.

ISA: 15°C at sea level - 30°C = -15°C at FL150

Poor, because the sweep-back design has the effect of reducing the lift capabilities of the wing.

For a commerical aeroplane: During take off. At this point the aircraft has it it's maximum weight, and accelerating in the vertical plane requiring the highest ammount of lift to counteract the weight.

V1 is lower when the runway is wet than when the runway is dry, because of the longer ASDR on a wet runway.

35 ft

For Reference:

• 50ft for Class B or A (<15° AoB at take-off or normal landings)

• 35ft for Class A (dry take-off or steep approach)

• 15ft for Class A (wet take-off)

Fusible plugs offer protection from tire blowouts caused by thermal expansion that is generated in the tire under extra hard braking conditions.

IRS / GPS / VOR / DME

An orographic cloud is formed as the air rises up the slope and will often envelope the summit.

When the air is humid, some of the moisture will fall on the windward slope and on the summit of the mountain.