KARACHI: The captain of the passenger jet that crashed in the hills of Islamabad on Wednesday was a top professional flying into one of the most testing airports for pilots, a colleague said.

"Islamabad airport's location is not an easy destination to fly into," Hashim Raza Gardezi, a former colleague of Pervez Iqbal Chaudhry who piloted the doomed Airbus A-321, said.

The craggy Margalla Hills to the north of the capital and unpredictable wind patterns can make an approach extremely difficult he said, going so far as to describe Islamabad as "one of the worst weather conditions in the world".

"Irregular wind systems surround the Margalla Hills often make it difficult for the pilots while in the air," Gardezi, a pilot for state Pakistan International Airlines (PIA), said.

Flight 202 from Karachi was coming into land at Benazir Bhutto International airport when witnesses saw a jet flying at unusually low altitude then heard a loud boom.

Gardezi said that Chaudhry, was a true professional.

"Chaudhry was one of the finest professionals in this field... who never took unnecessary risks during his professional career."

Procedures for safe landing at Islamabad advise pilots not to descend lower than 1,000 feet (300 metres) unless they have full visibility of the runway.

Gardezi said half an hour before the crash, a PIA flight was diverted to the eastern city of Lahore owing to poor weather conditions.

"With the experience Chaudhry had, I suppose the weather had got better by then prompting him to go for landing," he told Geo television.

Pakistan's Civil Aviation Authority (CAA) said the pilot had been in contact with the control tower at the airport until just before the crash.

"In the last conversation with the control tower, the pilot had been given landing clearance and the plane was proceeding normally for landing before it crashed into the hills," said Riaz-ul-Haq, the authority's deputy director.

The civil aviation authority said all possible causes would be investigated, including terrorism and bad weather, although officials gave no indication that an attack might have been to blame.