QUITO, Ecuador -- Before horrified air traffic controllers watched a Cubana Airlines jetliner careen off a runway and slam into a neighborhood, killing 79 people, they had no inkling that there was trouble aboard the aircraft.
``The crew maintained normal dialogue with the control tower, just the strictly necessary conversation of a normal takeoff,'' said Civil Aviation chief Oswaldo Dominguez.

But as Ecuadorean air safety officials on Sunday probed deeper, they discovered that something went fatally amiss before Saturday's crash.

Cubana pilot Mario Ramos skidded the Tupolev-154 some 2,600 feet along the runway in an attempt to abort the takeoff. But the 148-seat, Soviet-made plane smashed through a retaining wall, clipped the roof off an auto repair shop and erupted in a fireball, killing 69 of the 90 persons aboard and 10 others on the ground.

Amid the charred wreckage, heavy with the odor of jet fuel, rescuers found the Tupolev's two voice and flight data recorders. Dominguez said Sunday night that he would send the two recorders to Cuba for analysis.

When it crashed, the Cubana Airlines flight, with 76 passengers and 14 crew members aboard, was leaving Quito's Mariscal Sucre Airport for Guayaquil and was to continue on to Havana. Most of the fatalities were Cuban crew members or Ecuadorean tourists headed for vacation in Cuba, although the victims included two Italians, a Jamaican, two Chileans and a Spaniard.

Among the victims were two great-grandchildren of Ecuador's most renowned artist, painter Osvaldo Guayasamin. The youngsters, 4-year-old Alejandra Sule and 4-month-old Martin Sule, were also the grandchildren of Anselmo Sule, Chile's Radical Party leader and a former legislator. The children were traveling with their mother, Maita Madriñan Guayasamin, who also died.

A small sign of trouble occurred after the flight arrived in Quito from Havana at 10:46 a.m. The flight engineer and two mechanics worked to repair a jammed air valve in one of the jetliner's three turbines, Dominguez said. They reported the problem fixed.

Since no other airline in this hemisphere uses Soviet-made aircraft, Cubana usually takes along its own Soviet-trained mechanics for repairs en route.

What prompted the crew to brake on the runway as the Tupolev took off again at 1:03 p.m. remains unclear.

``There are signs that the motors were put in reverse,'' Dominguez said.

``What we are trying to discover is why the crew tried to abort the takeoff. It is not normal. . . . The plane never got off the ground.''

Cuban officials told Dominguez the jetliner was built in December 1985 and had 9,256 hours of flight time. Records brought from Cuba showed adherence to all maintenance requirements, he added.

``The plane was totally in compliance. There are records of all the inspections and obligatory maintenance procedures,'' he said.

Cubana Airlines' fleet of aged Tupolev and other Soviet-made aircraft has suffered since the collapse of the Soviet Union. Spare parts are hard to come by and must be paid for in scarce U.S. dollars. Havana's Jose Marti International Airport has several Tupolevs and other Soviet-era aircraft on the tarmac being cannibalized for parts.

Dominguez discarded any possibility that a bomb or other terrorist act could have caused the crash.

A day after the crash, huge cranes and tractors hauled parts of the charred fuselage to a hangar as residents stood nearby amid twisted metal and burned grass.

Several residents of Quito's working-class Rosario neighborhood recounted their shock at seeing the jetliner barrel through a retaining wall and onto a soccer field, crushing 36 grazing sheep.

``It never took off. It just came crashing through everything,'' said Jose Sarango, 35, a psychology student. ``People didn't die from injuries. They died from the explosion and fire.''

Flames leapt some 150 feet into the air after the crumpled fuselage came to a rest abutting a 30-foot-high tower of approach lights. Residents sought to rescue passengers, but many were kept away by intense heat.

``The passengers were shouting, `Help!' But then the final explosion came and everything was quiet,'' said Jorge Guzman, 27, a local resident.

Herald staff writer Juan O. Tamayo contributed to this report.