Passenger plane in security alert

The flight from Lahore had 81 passengers on board

A jumbo jet flying to the UK from Pakistan was tracked within 40 miles of Manchester by two RAF fighters during a security alert, the BBC has learned.

It was sparked after UK air traffic controllers said they could not contact the Pakistan International Airlines (PIA) flight from Lahore last Friday.

The RAF jets were scrambled as the 747 with 81 passengers on board flew towards Manchester Airport.

The pilot eventually made contact and the plane landed safely.

An investigation by BBC GMR has discovered that air traffic controllers in Maastricht lost contact with flight PK709 as it headed from Northern Europe to the UK.

We responded to an alert from the aviation authorities and we responded appropriately Ministry of Defence

It should have made contact with UK air traffic control as it crossed the North Sea but National Air Traffic Services (NATS) said no communication was made.

The RAF planes flew alongside it from the Lincolnshire coast to an area 40 miles (64km) from Manchester.

The pilot then contacted air traffic control and landed the plane 20 minutes later.

The airline said the pilot and crew were unaware that fighter jets had been scrambled and that anything unusual was happening.

Captain Shuja Naqvi of PIA said the pilot was not to blame.

"The pilot would only realise that there is no communication if he ceases to hear other airplanes for any significant length of time.

"But the first officer told me they could hear other airplanes talking to the ground and amongst themselves so my understanding is that they would not suspect the radio had packed up."

Another spokesman also claimed the plane had been unable to contact air traffic controllers in Manchester but had spoken to operators in London.

NATS has disputed this, saying it would not have launched a security alert if the plane had made contact.

The plane landed safely at Manchester Airport

NATS has filed a report on the incident with the Civil Aviation Authority, and PIA has mounted its own inquiry.

A spokesman for NATS said: "The plane had not made contact with controllers at Maastricht.

"When the Maastricht people handed the plane over to us at Swanwick they told us they had been trying to get in touch with the plane for some time.

"The plane failed to get in touch with as required and we followed our standard procedures in alerting the security forces.

"We reported the incident to the Civil Aviation Authority (CAA) and its safety regulation group are now looking into it."

A spokesman from the Ministry of Defence (MoD) said the jets were scrambled as part of a "standard contingency plan".

"We can confirm that we were alerted by NATS at 1550 last Friday, as routine practice," said the spokesman.

"Two military aircraft escorted the flight to Manchester. At 1605 we were able to establish contact with the aircraft, and it landed at its intended destination.

"We responded to an alert from the aviation authorities and we responded appropriately."