Passenger steps into co-pilot's shoes mid-air!

But when mid-air a co-pilot of a Frankfurt-bound plane fell ill, the crew wished for a pilot among the passengers and to their surprise found one, who took on the duty.

As the co-pilot of a Boeing 747 was struck down with a severe migraine mid-air on Monday, the crew held out no hope there might be a "pilot on the plane".

Fortunately, their prayers were answered as one of the passengers, who works for North American Airlines, got up to reveal he was fully qualified to fly a jumbo jet, the Daily Mail reported.

With the co-pilot incapacitated, the heroic stranger stepped in to help the captain safely land the plane, with 264 passengers on board, as it was diverted to Dublin Airport.

The licensed Boeing 767 captain with North American Airlines had been travelling as a passenger on the Lufthansa 747 flying from Newark to Frankfurt on November 19.

Flight landed safely in Dublin at about 5.30am (local time), Dublin Airport Authority (DAA) confirmed.

The co-pilot was hospitalised and the flight continued after a six-hour delay to allow a replacement crew to fly in.

A Lufthansa spokeswoman said the man who stepped in was fully licensed to operate and fly the 747.

"In such circumstances it's absolutely normal procedure for the pilot, the flight captain, to continue to operate the aircraft," she said.

"Also, where necessary, the cabin crew are fully trained and can be called upon to read checklists back to the pilot. The procedures are in place for such an eventuality. But the effort of the off-duty pilot were certainly appreciated," she added.

The Irish Aviation Authority (IAA) has been notified of the incident and has received a briefing report.

The Air Accident Investigation Unit (AAIU) of Ireland's Department of Transport has been notified and is investigating. Experts from the AAIU attended the plane after it touched down in Dublin.

"Whenever you have any sort of medical issue on board, whether it's a doctor or appropriately qualified person, that's always appreciated," the spokeswoman said.

"The flight would have been operated as per procedures and safely even if the off-duty pilot had not been there," she added.