Distress and urgency messages

Any distress or urgency message must be as short, full and clear as possible. Every station received this kind of message should retransmit it to the ATC unit immediately and the controller must acknowledge it at once.

An emergency message is usually transmitted on frequency-in-use, but special emergency frequencies can also be used.

A distress message begins with the word “Mayday” pronounced 3 times and consists of:

1. ATC unit call sign;

2. identification of the aircraft;

3. nature of the distress condition;

4. intentions;

5. position, level and heading of the aircraft;

6. any other useful information.

All station received the message should monitor the frequency and the controller will impose radio silence with the phase: “STOP transmitting”, addressed to all or one particular station.

When the aircraft is no longer in distress, it cancels Mayday.

The controller cancels silence with phase “Distress traffic ended”. It means resuming of normal communication operations.

Urgency message starts with signal “PAN PAN’ 3 times and includes:

1. ATC unit call sign;

2. identification of the aircraft;

3. the nature of urgency;

4. intentions;

5. other useful information.

Urgency messages have priority over other except distress messages. Nobody may interrupt them.

The mysterious black box

There is a story that is retold whenever a plane crash hits the headlines; if only the aircraft were made of the same material as the black box, then everybody would survive. The legendary invincibility of the famous box is familiar to most of us. Yet for such a well-known object, it is remarkably mysterious. How many of us know that the “black” box is in fact painted fluorescent orange?

“It was originally called a black box in the days when anything to do with electronics was new and strange” explains Pete Cook from a flight recorder manufacturer. “They are painted orange nowadays to make them more easily visible in the event of a crash”.

There are two kinds of black box; the flight data recorder (FDR) and the cockpit voice recorder (CVR). Both are normally stored at the rear of an aircraft, where the fuselage meets the upper tail fin – the part of planes that has the best survival record. The same principle applies to human passenger – you are safer at the back.

Despite their reputation, neither box is in fact indestuctible. However, they can withstand a temperature of 1,100°C for 30 minutes and 250° for 10 hours. They must also be able to survive an impact force of 3,500g – that is 3,500 times the force of gravity.

To take this kind of strain, flight recorders are encased in two thicknesses of titanium. Memory chips hold the flight data.

While FDRs make an electronic record of a plane’s mechanical performance, CVRs record the communication between the crew. “After a crash in water, they send out a sonar “ping” so that they can be found”, says Cook. But they are still only recovered in 80 per cent of accidents”.