SEATTLE -- A Navy Boeing 707, returning from a test flight designed to push the craft beyond its design limits, landed safely Thursday with portions of its rear vertical tail and right rudder missing, officials said.
Boeing officials said the plane, which is the prototype of 16 707s the company is making for the military, took off from Boeing Field in Seattle about noon for a flight to Bellingham and back.
The plane lost about one-third of its vertical tail fin and a small part of its right rudder while a Boeing test pilot was conducting a 'flutter' test on the plane over the Olympic Peninsula, a test designed to push the airplane beyond its design limits.
A Boeing spokesman said the pilot had no difficulty flying or landing the plane after the incident occurred.
Shortly after the plane landed at 3:40 p.m. Thursday, it was pushed into a hangar as technicians swarmed over it, looking for more damaged parts and possible clues to the cause of the incident.
'We have no idea what went wrong at this point,' said Boeing spokesman Elliott Pulham.
The plane is dubbed the E-6A by the military, a modified version of the 707 that is crammed with communications gear and used for various purposes, including as a link between national military authorities in the event of a nuclear war.
The plane was built by Boeing's Commercial Airplane division, which has been under close scrutiny recently because of alleged quality control problems.
Pulham said the 'flutter' test involves the plane going into a 'rapid descent at 530 mph to put as much pressure as possible on the surfaces of the plane.
'The pilot then tests some of the moving parts to see how they react,' Pulham said. 'It was during this procedure, at the heighth of the stress test, that the tail snapped.'
Pulham said the crew of three heard a popping sound and 'a thud' and immediately turned toward home.
'The pilot was in complete control of the plane all of the time,' Pulham said. 'They knew they had a problem, but they didn't know what exactly was wrong until they got on ground and looked at it.'
A private pilot who landed just ahead of the damaged plane said the pilot did a 'first-class flying job.'
A farmer living about 10 miles north of Centralia said he heard a boom and looked up and saw pieces of what were apparently pieces of the plane's tail falling to the ground. Centralia is southeast of the Olympic Peninsula.
Boeing is now testing six of the 16 E-6As to be delivered to the Navy, with the one involved in Thursday's incident having undergone tests since 1987.
One of those E-6As being tested lost a mile-long antenna wire and a 47-pound drogue -- a funnel-shaped device that helps pull the antenna behind the plane -- Sunday while flying over eastern Washington. The antenna and drogue still have not been found.
Boeing has delivered more than 700 of the 707s for commercial passenger use. One of those planes crashed last week on Portugal's Azore Islands, killing more than 140 people. Investigators are still trying to determine the cause of that crash.
