Control of Aircraft — Page 343, Lesson 462

Let's pick up with the emergency side of air traffic control — the situations where normal procedures give way to immediate action. I want to walk you through four specific cases: emergency contact, emergency descent, fuel jettison, and strayed or unidentified aircraft. First, emergency contact. In an emergency, pilots can expect ATC to contact them on 121.5 MHz. That's the international VHF distress frequency — the one you'd monitor when things go wrong. As a back-up, ATC may use the inter-pilot air-to-air frequency, 123.45 MHz. That's the frequency pilots use to talk to each other, not normally to ATC, but in an emergency it serves as a secondary channel. So remember the primary is 121.5, the back-up is 123.45. Now, emergency descent. This applies when an aircraft suffers a pressurization failure at altitude. The rules require the aircraft to be descended to an altitude where oxygen in the air supports life — in other words, down to a level where the air is breathable without supplemental oxygen. When this happens, ATC will broadcast a warning to other aircraft in the vicinity of the descending aircraft. And here's the key responsibility for the pilot of the descending aircraft: they should attempt to broadcast the aircraft's altitude at intervals. Why? To assist other aircraft to avoid a collision. The descending aircraft is coming down fast through other traffic's levels, so announcing altitude repeatedly gives everyone a chance to get out of the way. Next, fuel jettison. This is about reducing the aircraft's mass. In certain circumstances, it may be necessary to reduce the mass to maximum landing mass as soon as possible — that's the heaviest the aircraft is certified to land at. You do this by dumping as much fuel as is required. Now, here's the requirement: all aircraft which have a maximum take-off mass greater than the maximum landing mass are required to have a fuel jettison system. So if the aircraft is too heavy to land safely, it must be able to dump fuel. There are specific conditions for jettisoning. If the aircraft is flying in CAS — that's controlled airspace — before commencing fuel jettison, the controlling ATCU is to be informed. ATCU is the air traffic control unit. The route over which the fuel is to be jettisoned should be clear of towns, preferably over water, and clear of areas where thunderstorm activity has been reported or is expected. The level at which the jettison takes place is to be not lower than 6000 ft. Why that height? It allows the fuel in aerosol form to evaporate before reaching the ground — so it disperses safely rather than raining down. And finally, the ATCU is to be advised of the duration of the operation — how long the jettisoning will take. Finally, strayed and unidentified aircraft. These are two distinct definitions. A strayed aircraft is one that has deviated significantly from its intended track, or reports that it is lost. So it's a navigation problem — the aircraft doesn't know where it is relative to where it should be. An unidentified aircraft, on the other hand, is one of which the ATCU is aware, but the identity is not known. So ATC can see it on radar, but they don't know who it is — no call sign, no flight plan match. Strayed is about position; unidentified is about identity. That's the full picture of these emergency control procedures. Let me know if you want to dig into any of these further.