The UK’s National Air Traffic Services (NATS to its friends) recently issued a DVD about ‘level busts’. This is when a pilot inadvertantly flies higher or lower than than her assigned altitude. The problem, which is very common, raises safety concerns. As an instrument-rated pilot myself, I would like to avoid level busts if I can.

A typical scenario described on the video is this: a controller clears a plane to 11,000 feet (”Fastair 345 climb flight level one one zero”). The pilot read back the instruction but dialed 10,000 feet into the autopilot and nearly hit another aircraft at that level.

It looks like an easy mistake to make but there are a number of things that contribute to the error including pilot workload (flying the plane, reading charts etc.), pilot expectations (he was probably expecting 10,000 feet) and habit (getting a clearance and setting the autopilot are frequent repetitive tasks that most pilots do correctly 99.99% of the time).

What is interesting for Bad Language in this whole analysis is the use of a very strictly defined vocabulary and templates for communication on the radio. For example, when a controller wants you to climb to flight level 100, he will instruct you to “climb flight level one hundred” but for any other level he will spell out the numbers, e.g. flight level two four zero.

A similar discipline exists in radio use in the army. Radio operators will use the phrase “say again” rather than “repeat” if they didn’t understand a transmission. Why? Because “repeat” is the word used when you want the artillery to fire another load of shells at the same place they fired at last time. Which may not be exactly what you wanted.

voiding misunderstandings. But even when lives depend on it, you cannot guarantee that everyone will understand what you say all the time. I think this is a powerful lesson in the ineffability of language and the importance of saying what you mean and meaning what you say.