FRIDAY'S televised shots of two light aircraft flying under the Ballachulish Bridge and the recent report of a helicopter buzzing around under the Skye bridge illustrate that Biggles is still alive and well and flying somewhere in Scotland. Flying under bridges has always been a temptation to pilots. The kudos is usually well worth the fine if you are the first and only one to get under a worthwhile bridge.

Some time ago an RAF officer wanted to get out of the service because he was going to be taken off flying duties. A job with a major airline was his if he could get out of the RAF quickly, so to facilitate his discharge he flew a Hawker Hunter up the Thames and under London Bridge. The press had a field day. Was this the sort of man the taxpayer was paying millions of pounds to train? The RAF's selection and training procedures were called into question.

It did not, as you might think, immediately kick the pilot out of the junior service. That would have been a public admission of mistakes on its part. Instead, it put him into a psychiatric hospital. That satisfied the critics as even the most excoriating of them accepted that only a ''head case'' would fly a fast jet under London Bridge. Little did they know. After the hullabaloo abated the RAF pushed the pilot out of a side-door on a wet day back to civilian life.

Notwithstanding the foregoing, there is safety in numbers. After the Forth Road Bridge was constructed back in the 1960s, it was realised in aviation circles that it would he only a matter of time before someone would fly under it. It was not long before the senior service took up the challenge, and did so in spectacular fashion.

In the early hours of a dark winter night and under cover of darkness, four Fleet Air Arm Blackburn Buccaneers out of Lossiemouth on a low-level night sortie came in from the North Sea off by the Isle of May. They swept up the Forth estuary line astern and flew under both bridges.

This daredevil escapade was not reported in the press as nobody saw it happen. You do not get a lot of time to see four Buccaneers in a hurry, especially in the dark and when you are least expecting them.

Those in the local area whose sleep did not survive the racket thought they had been wakened by thunder or that the chemical plant at Grangemouth had blown up, but it was the insomniacs among them who were delivered the full impact of the event and who found out just how ear-splitting eight Rolls-Royce Spey engines at maximum thrust could be. The entire Forth basin shook with the noise. It was a night not easily forgotten.

The ''brass'' were soon apprised of what had happened and it did not take them long to find out who were responsible, but the Navy could not afford to get rid of eight of its front-line officers (two in each aircraft) or even suggest that they were all mad, so the incident was put down to high spirits and the sort of stuff which won us the Battle of Britain. Tally-ho, chaps.

Stewart Gellatly,

1 Greepe,

Dunvegan,

Isle of Skye.