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.

Those are contrails.

The jet engine exhaust gases consist of carbon dioxide and water vapour.

At high altitudes the wator vapour gets released in a very cold environment. This can cause the air to be saturated with water vapour and then condenses. If cold enough the condense can freeze into white droplets. This forms the contrails.

Occluded fronts are formed during the process of cyclogenesis when a cold front overtakes a warm front. When this occurs, the warm air is separated (occluded) from the cyclone center at the Earth's surface.

Occluded fronts usually form around mature low pressure areas.

The weight of an aircraft is applied at the CG. The lift at the CP. The relative position between these 2 points determines the stability of the aircraft. For an Aircraft with a tail surface, a CG in front of the CP constitutes a stable system, while a CG behind the CP an unstable system.

A precision approach uses both lateral (from left to right) and vertical guidance. A non-precision approach only uses lateral guidance.

The distance from the datum to the point at which the weight of a component acts.

You will need to have a clearance, to be stable and visual.

Because the specific gravity can change with temperature.

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.

Their formation is most often triggered by freezing water vapour from the exhaust of aircraft engines.