Introduction — Page 127, Lesson 108

I want to walk you through the IFR communications section now. This chapter focuses on the communication procedures that apply specifically to IFR flight — that's Instrument Flight Rules — rather than the procedures that apply to both VFR and VFR. The book notes that most procedures for IFR and VFR are actually identical, but some words and procedures are generally only used by large commercial aircraft, so they appear in this section. Let's start with call signs and the use of the word 'HEAVY'. Aircraft that are in the heavy wake turbulence category must use the word 'HEAVY' in the initial call to an ATSU — that's an Air Traffic Service Unit. So if you're flying an aircraft that qualifies as heavy, your first call to any ATC unit includes that word right after your call sign. For example: "Brize Radar, Speedbird 213 Heavy, request radar advisory." Now, how is the heavy wake turbulence category determined? It's normally determined by maximum certified take-off weight. The threshold is greater than 136,000 kilograms — that's the figure you need to remember. If your aircraft's maximum certified take-off weight exceeds that, you are in the heavy category and must use 'HEAVY' in your initial call. Next, let's look at change of call sign. In the interests of safety, an aeronautical station — that's ATC — may tell an aircraft to change its call sign temporarily. The aircraft station cannot do this on its own; only ATC can instruct the change. Why would they do this? For example, there might be two aircraft on the same frequency with similar-sounding call signs, like Speedbird 123 and Birdseed 123. That could cause confusion. So ATC might say: "Speedbird 123 change call sign to BA 123." When the confusion is no longer a problem — for instance, one aircraft has left the frequency, or the subject aircraft is handed over to another agency — the aircraft is told to revert to its original call sign. The phrase would be: "BA123 revert to flight plan call sign." Now let's move to level reporting — how you report your vertical position. The reporting of vertical position depends upon the altimeter pressure setting in use. There are three pressure settings we need to understand: Standard Pressure Setting, QNH, and QFE. First, Standard Pressure Setting, or SPS. Its reading is based on sea level pressure in the standard atmosphere — that is, 1013 hectopascals. When you set SPS, your altimeter reads FLIGHT LEVEL. Important note: SPS does not read height above sea level; it merely reads above a standard datum. So flight levels are based on this standard pressure setting. Second, QNH. With this pressure setting, the altimeter reads ALTITUDE above mean sea level for the actual atmospheric conditions. So QNH gives you your actual altitude above sea level, accounting for the real air pressure at the time. Third, QFE. With this pressure setting, the altimeter reads HEIGHT, usually above the runway threshold. The book notes that commercial operations rarely use this pressure setting now. So levels may be reported as Altitude, Height, or Flight Level, depending on the phase of flight and the altimeter setting in use. The key rule: with the Standard Pressure Setting set, the words 'Flight Level' must be used prior to the given level. So you don't just say "descend to 120" — you say "descend to Flight Level 120." Let me show you the examples from the table. In these examples, 'climb' and 'descend' are interchangeable — the same phrase structure works for both. For a Flight Level change: ATC says "Fastair 243, Descend to FL120." The pilot responds "Descend to FL120 Fastair 243." For another Flight Level change: ATC says "Fastair 243, Recleared FL60." The pilot responds "Recleared FL60 Fastair 243." For an altitude change: ATC says "Fastair 243, Set QNH 1003, Descend to 3000 ft." The pilot responds "QNH 1003, Descend to 3000 ft Fastair 243." And for an inability to climb: ATC says "Fastair 243, Expedite climb to FL200." The pilot responds "Fastair 243, Unable due to weight." Notice in that last example, the pilot acknowledges the instruction but states the reason they cannot comply — in this case, due to weight. That's a standard way to handle an inability to comply with an ATC instruction. That figure shows you the pressure settings examples visually. So to summarise: your vertical position reporting depends entirely on which pressure setting you have in your altimeter — SPS gives you Flight Level, QNH gives you Altitude, and QFE gives you Height. And if you're heavy, don't forget to say 'HEAVY' in your initial call.