The headline "Engine-failure 777 busts ETOPS limit" (Flight International, 25-31 March) is slightly misleading in its assertion that a United 777 "bust" the ETOPS limit. ETOPS diversion limits are predicated upon "still-air" distances, not on current conditions. Therefore, from a legal standpoint, the crew were in full compliance with the law.

Regulations are being increasingly formulated upon performance, as opposed to prescriptive criteria. This provides a good example of the performance exceeding the prescription and being superficially illegal, also known as "captain's judgement".

If the captain of this flight were to apply "still-air law" to the prevailing flight conditions (with its stronger-than-forecast headwinds), he would have had to perhaps make a less than optimum landing, been convicted of willful negligence and the law would be shown to be an ass. A lose-lose result.

David Connolly Brussels, Belgium

Source: Flight International