Ryanair is threatening to sack pilots after being criticised by air accident investigators over a series of dangerous approaches to airports. In the latest incident to emerge, an aircraft flew so low over rooftops that it triggered two warnings in the cockpit and sixteen complaints from alarmed residents.

It was the third serious incident in less than a year, and the fourth in two years, involving a Ryanair jet approaching an airport too fast or at the wrong height and being forced to abort landing.

All Ryanair staff are under pressure to meet turnaround times of only 25 minutes, the tightest in the industry, and pilot unions say that this can lead to mistakes.

British Airways and easyJet said that there had been no similar incidents involving their aircraft in the past two years.

Michael O’Leary, the Ryanair chief executive, has responded to the incidents by issuing a memo to all pilots telling them that they will be demoted the first time they make a dangerous approach and sacked for a second offence.

The memo, a copy of which has been obtained by The Times, states that a new disciplinary procedure is being introduced in response to a series of “high energy approach incidents over the past two years”.

Pilot unions said that the memo would force the problem underground, leaving pilots too frightened of losing their jobs to cooperate with efforts to find out why the incidents were happening.

The Irish Air Accident Investigation Unit last week issued a report on the third incident, which involved a flight carrying 134 people from Stansted to Cork on June 4 last year.

As the aircraft approached Cork, the captain realised that he was too high to make a safe landing. The co-pilot advised him to perform a “go-around”, which would involve the aircraft flying straight ahead and climbing to 3,000ft before beginning a new approach.

But the captain decided to fly in a tight circle to lose height and land only minutes later. He banked so hard that he exceeded the normal operating limit for tilting the Boeing 737’s wings. The captain ignored repeated warnings from the co-pilot that he was losing height.

The aircraft came within 425ft of the ground as it passed over the suburbs of Cork and the cockpit “ground proximity” alarm sounded twice.

The report said the “serious incident” was caused by the captain failing to comply with standard procedures and ignoring the advice of the co-pilot.

It referred to a previous incident, on March 23, 2006, when another Ryanair aircraft only “marginally avoided” crashing during an approach to Knock, in western Ireland. The unit criticised the airline for failing to report the incident for almost two weeks, by which time some evidence had been deleted.

Captain Evan Cullen, the president of the Irish Airline Pilots Association, said: “The link is the pressure pilots are under. Everybody at Ryanair is under pressure to meet very tight turnaround times.”

In the most serious incident, in September 2005, a Ryanair co-pilot had to take emergency control of an aircraft approaching Rome after the captain suffered a breakdown.

Ryanair, which yesterday announced record quarterly profits, declined to answer questions on the incidents.

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