GRAMMATIKO, Greece (AP) -- The F-16 pilots were confronted with a chilling sight.
At an altitude of 34,000 feet (10,363 meters) over the Aegean Sea, they peered into the cockpit of the jetliner packed with vacationers - and saw nobody at the controls.
Minutes later, the Cypriot jet slammed into a mountainside north of Athens on Sunday after at least one pilot lost consciousness from lack of oxygen, killing all 121 people aboard. More than a third of those killed were children.
The cause of Greece's deadliest plane crash appeared to be technical failure - resulting in high-altitude decompression - and not terrorism, authorities said. A transport official said the 115 passengers and six crew may have been dead when the plane went down.
Helios Airways flight ZU522 was headed from Larnaca, Cyprus, to Athens International Airport when it crashed at 12:05 p.m. (0905 GMT) near Grammatiko, a scenic village 25 miles (40 kilometers) north of the Greek capital. Flaming debris, luggage and bits of human remains were strewn across two ravines and surrounding hills.
Family members wept in anguish as they waited at the Athens and Larnaca airports. When news of the crash emerged at Larnaca, relatives swarmed the airline counters, shouting ''murderers'' and ''you deserve lynching.''
A man whose cousin was a passenger told Greece's Alpha television he received a cell-phone text message minutes before the crash. ''He told me the pilots were unconscious. ... He said: ''Farewell, cousin, here we're frozen,'' Sotiris Voutas said - indicating the plane was cold, a sign of decompression.
About a half-hour after takeoff, pilots reported air-conditioning system problems to Cyprus air traffic control. Within minutes, after entering Greek air space over the Aegean, the Boeing 737 lost all radio contact. Two Greek F-16 fighter jets were dispatched soon afterward.
When the F-16s intercepted the plane, jet pilots could see the co-pilot slumped over his seat. The captain was not in the cockpit, and oxygen masks dangled inside the cabin, government spokesman Theodoros Roussopoulos said.
He said the jet pilots also saw two people possibly trying to take control of the plane; it was unclear if they were crew members or passengers. The plane apparently was on automatic pilot when it crashed, Helios spokesman Marios Konstantinidis said in Cyprus.
''When a pilot has no communication with the control tower, the procedure dictates that other planes must accompany and help the plane land. Unfortunately, it appeared that the pilot was already dead as was, possibly, everyone else on the plane,'' Cyprus Transport Minister Haris Thrasou said.
A witness described the instant the airline smashed into the 1,500-foot (457 meters)-high mountain, flanked by the F-16s. ''We saw some fighter jets flying very low and after a few minutes we heard a very loud noise and saw pieces of the plane flying in the air,'' said Spyros Papachristou.
The head of the Greek airline safety committee, Akrivos Tsolakis, said the crash was the ''worst accident we've ever had.'' He said the plane's black boxes had been recovered, containing data and voice recordings valuable for determining the cause
''There apparently was a lack of oxygen, which is usually the case when the cabin is depressurized,'' Tsolakis said.
The F-16 jets met the plane at 34,000 feet (10363 meters), the Greek air force said. At that altitude, the effects of depressurization are swift, said David Kaminski Morrow, of the British-based Air Transport Intelligence magazine.
''If the aircraft is at 30,000 feet (9144 meters), you don't stay conscious for long, maybe 15 to 30 seconds,'' he said. ''But if you are down at 10,000 feet (3048 meters), you can breathe for a lot longer.''
The flight was to have continued to Prague, Czech Republic, after stopping in Athens. This is the height of Europe's summer travel season, when Mediterranean resorts like Cyprus are packed with tourists. The area was likely to be particularly crowded, because Monday is a national holiday in Greece and Cyprus.
There were 48 children aboard, mostly Greek Cypriots, Helios spokesman Giorgos Dimitriou said in Athens.
Greek state television quoted the Cyprus transport minister as saying the plane had decompression problems in the past. However, Helios representative Dimitriou said the plane had ''no problems and was serviced just last week.''
Liz Verdier, a spokeswoman for Boeing, said the 737s, like all Boeing planes, are equipped with warning systems that alert pilots when decompression is occurrring. However, she could provide no details about how the warning system works on the 737.
On Cyprus, several callers to radio and television programs said they experienced severe air-conditioning problems on Helios jets in recent months. Some said the cabin was freezing and the crew provided blankets; others said it became unbearably hot.
In June 2000, a Boeing 737-200 of the Canadian carrier WestJet lost cabin pressure because pilots mistakenly shut down auxiliary power. Cabin altitude reached 24,000 feet (7315 meters) before the plane descended and pressurization became normal. None of the 118 passengers was injured.
At the Greek crash scene, more than 100 firefighters, backed by planes and helicopters dropping water, fought a brush fire caused by the crash. The plane was in at least three pieces: the tail, a bit of the cockpit and a piece of fuselage that witnesses said contained many bodies. Sections of the plane were ablaze.
Fire department rescue vehicles carried body bags up the steep slopes of the charred valley to a fleet of ambulances. None of the bodies had masks on their faces, the fire department said. Black-robed Greek Orthodox priests were on hand.
''There is wreckage everywhere. Things here are very difficult, they are indescribable,'' Grammatiko Mayor George Papageorgiou said.
The remains of many victims were charred beyond identification, and the Cyprus transport minister said DNA tests would be necessary.
Greek Prime Minister Costas Caramanlis canceled a holiday on the Aegean island of Tinos to return to Athens. The Cypriot president also canceled a vacation.
Helios Airways, Cyprus' first private airline, was founded in 1999. It operates a fleet of Boeing 737s to cities including London; Athens; Sofia, Bulgaria; Dublin, Ireland; and Strasbourg, France. EU newcomer Cyprus is divided into Turkish and Greek sectors. Most of its 800,000 people are Greek Cypriots.
Associated Press writers Derek Gatopoulos in Grammatiko; Petros Karadjas in Larnaca, Cyprus; Ondrej Hejma in Prague, and Mara D. Bellaby in London contributed to this report.