Not all Sea Kings are equipped for night vision goggles

Mr Hoon is being questioned over why the pilots of two Sea King helicopters that crashed in Iraq last year were not equipped with the goggles.

They look like a pair of mini-binoculars and are attached to a pilot's helmet.

To use them, the lighting has to be compatible in the aircraft cockpit and the instruments covered in phosphorus.

So what difference do they make?

"If it's absolutely pitch-black, none whatsoever, but if it's like that you are not flying anyway," one ex-Sea King pilot told BBC News Online.

"If there's any light whatsoever they would make the difference between not being able to see and being able to see.

THREE SEA KING TYPES Anti-submarine helicopter Commando aircraft Surveillance helicopter MP questions Hoon over Iraq crash

"It's like standing on the middle of Dartmoor and the difference between there being a new moon or a full moon.

"On a moonlit night you can see as well as in daylight with the new generation of goggles."

The pilot, who did not want to be named, spent about 200 of his 500 hours flying Sea Kings in the 1980s, including in the 1982 Falklands War, wearing night vision goggles.

The type of Sea King he flew were different to those involved in the Iraq crash, which were carrying out surveillance work.

Dual control

Disadvantages of flying with night vision include the total loss of peripheral vision and thus the potential for spatial disorientation.

The easiest and most common solution is for a second pilot to be present in the cockpit - Sea Kings are dual control - and then only have one pilot flying with night vision at any one time.

There are currently three types of Sea King used by the Royal Navy - they have the same standard helicopter body but do three different jobs:

• The Mark 6 anti-submarine helicopter - used for low-level flying above the sea

• The Mark 4 Commando Sea King, used mainly to transport Royal Marine troops, again flying at low-level

• The Mark 7, called the Airborne Surveillance and Area Control (ASaC) Sea King.

High altitude

A Ministry of Defence spokesman told BBC News Online the Sea Kings used for low-level flying did use night vision goggles.

But they had never been worn by pilots of the surveillance helicopters, which work at high altitude.

"It is specifically used as a tactical system," he said.

But the MoD was now looking at a recommendation from the board of inquiry into last year's Gulf crash for the goggles also being used for flight safety reasons.