Plane dropped thousands of feet in emergency over the Black Country

The pilot plunged from 25,000 ft, or 4.7 miles, to 10,000 ft, or two miles, over Dudley to stabilise the plane, after a faulty valve caused a loss of pressurisation inside the aircraft.

The aircrew donned oxygen masks and informed the 23 passengers about the problem on board the turboprop airliner.

An investigation was launched by the Air Accidents Investigation Branch, which investigators say was a 'serious incident'.

The aircraft became stable at 10,000 feet and the MAYDAY call was cancelled. The plane was flying from Manchester to Jersey

A total of 27 people were on board, with four aircrew present alongside the passengers.

The incident took place on December 8 at 07.18am.

The pilot continued flying at 10,000 ft until reaching Jersey after clearance was given by air traffic controller.

No other incidents took place and the plane made a safe landing.

The co-pilot was alerted to the loss in cabin pressure after warning signs came on inside the plane, and warned the pilot before the MAYDAY call began.

The warning signs remained on for seven minutes and 48 seconds before the pilot had dropped to 10,000 ft - more than half of the initial altitude - before the lights turned off.

The aircraft was a Bombardier (De Havilland Canada) DHC-8-402, a passenger plane which is designed for medium ranged flights.

Both the pilot and co-pilot described feeling 'slightly lightheaded' as the events unfolded, the report found.

It resulted in them suffering hypoxia - where a lack of oxygen reaches the tissues.

The report said: "The final approach into Jersey which was 'not up to the usual standard'.

"After landing the crew realised the significant effects that hypoxia had had on their performance.

"It is probable that the loss of pressurisation was gradual but maintained just within system limits during the climb to FL250 (25,000 ft).

"When the aircraft was established in the cruise at FL250, the cabin pressure altitude continued to climb over a period of two minutes until the warning level was reached.

"Although by no means debilitating in this case, it shows how quickly the flight deck crew appeared to suffer the early signs of hypoxia.

"There were no injuries to passengers or crew."

The pilot handed the controls to the co-pilot to start a descent.

The co-pilot initially used autopilot but switched to manual as he felt the descent taking too long.

This accelerated the aircrafts descent from 2,000 feet-per-minute to 3,500 feet-per-minute.

The plane's faulty outflow valve was replaced after the flight, and was later returned to service.