BOGOTA, Colombia (AP) _ The route was familiar, the crew was experienced. Why _ even after being warned he was off course _ did the pilot veer straight into a mountain face?

Investigators searched for clues Tuesday on a ridge in Bogota's eastern mountain range, pocked with the wreckage of the Ecuador-bound Boeing 727 that crashed Monday, killing 53.

Air traffic controllers in Bogota radioed the passenger jet, leased to Air France by the Ecuadorean military-run carrier TAME, when it failed to turn 90 degrees southward at a radio beacon 2,000 feet from the runway's end.

Pilot Jaime Vasconez acknowledged the communication _ but nonetheless proceeded eastward for two miles, slamming into fog-shrouded El Cable mountain just 150 feet below its 10,170-foot summit.

Vasconez and his Ecuadorean crew of 10 flew the Quito-Bogota-Quito route three times a week, officials said. They knew where the mountains were. So why not turn north or south to avoid the ridge?

``That is the very question that we are investigating. What happened?'' Col. Julio Alberto Gonzalez, deputy director of the civil aviation authority, told The Associated Press. He refused to speculate on the cause, but ruled out weather.

``The weather conditions were indeed not the best, but did permit enough visibility to operate,'' the agency said in a statement. There was some drizzle and fog over the mountain.

Climbing, Flight 422 hit the ridge at about 170 mph at 4:47 p.m, tearing most bodies into small, unidentifiable pieces strewn over a half-mile, along with thousands of pieces of wreckage. Only five corpses were found intact. Rescue workers estimated Tuesday they had collected the remains of about 15 people.

``There was no possibility that anyone could survive the impact. It is very likely that everyone died instantly,'' Gonzalez said.

Rescue workers scoured the site overnight. Police arrested two looters.

The Quito-bound jet carried 43 passengers, including two Colombians, a Briton, a Swede, a Honduran, six French, four Danish and six Italian citizens _ two of whom were on their honeymoon. The rest were believed to be Ecuadorean.

Gonzalez said a Colombian-Ecuadorean-French team would investigate the crash.

The flight data and voice recorder, badly mangled in the crash, will be flown to the National Transportation Safety Board in Washington because Colombia lacks the equipment to read it, Gonzales said.

Some eyewitnesses said the three-engine plane was making strange noises, as if its engines were laboring or ready to quit.

A spokesman for TAME, Marco Emilio Erazo, said the plane, which had arrived in Bogota from Quito an hour before taking off on the return trip, was in good condition.

Ecuadorean President Fabio Alarcon had traveled to last weekend's hemispheric summit in Chile on the same plane.

``It did not have flight fatigue in its parts and it was in perfect technical condition,'' Erazo told the AP. He could not provide the plane's exact age or hours of service.

Erazo said the pilot, Vasconez, had 6,000 flight hours to his credit and was a retired member of the Ecuadorean air force.

In Paris, the national pilots union criticized the leasing agreement Air France had with TAME. Many airlines in Latin America have been criticized for less-stringent safety standards.

Without directly accusing TAME of inferior safety standards, the union said ``these commercial accords always lead to the same thing: A passenger gets on a plane whose colors don't match the code on the ticket.''