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To explain why the baggage compartments were catching fire, the bureau men borrowed a DC-6, filled its No. 3 fuel tank with water dyed bright red and coated its belly with a material that will absorb dye. Taking it into the air, they pumped more water into the No. 3 tank, forcing it to overflow through a vent. When they landed, they found that the wind had whipped the overflowing water to the belly and dyed it red. Included in the reddened area was the air intake of the cabin heating system. Conclusion: gasoline sucked into the heater had started the fires.
High-Speed Stall? In the current Idlewild investigation, the CAB hopes for crash clues from the automatic flight recorder, which records time, compass heading, air speed, altitude and "g's" (acceleration) and is mandatory equipment on all jets. When found, it was flown to Washington for study at the Bureau of Standards, its aluminum tape hopefully undamaged. Interest was focused on the speed that it will show, because one theory points to what airmen call a "highspeed stall" as the cause of the accident.
The stalling speed of a 707 flying straight and level and loaded to 250,000 lbs. is about 196 m.p.h. with the flaps retracted. In a turn with the wings banked at 17 degrees, the kind that jets often make when climbing away from Idlewild's runway 31-L, the stalling speed goes up to about 215 m.p.h. A 707 flying below that speed is apt to lower a wing and dive toward the ground. According to competent eyewitnesses, this is what American's 707 did. The stall, if it was a stall, might have been caused by retracting the flaps, which give the wing extra lift, before the plane had reached flying speed. To be on the safe side, new regulations were issued telling pilots not to start raising their flaps until they have at least 400 ft. of altitude, and not to retract them completely during a climbing turn.
A stall caused by prematurely retracted flaps would be due to pilot error, and in the opinion of CAB men, the crew that died at Idlewild was unusually competent; Captain James Heist had 18,000 hours, of which 1,600 were in 707s. So other theorists suspect that the fatal plunge of the 707 may have been caused by misbehavior of its hydraulic control system. There have been many instances, both proved and suspected, when the hydraulic system has made the aircraft extremely difficult for the pilot to control. This seems to have happened when a Sabena (Belgian) Airlines 707 crashed at Brussels in February 1961, killing 18 members of the U.S. figure-skating team. Though the
Belgian government has said nothing, it is an open secret in Washington that when Sabena's 707 nosed up sharply and fell in a whirling stall, its controls were found locked in full nose-up position.