TCAS incident at PDX

From:         richn@vcd.hp.com (Richard Nute)
Date:         20 Mar 94 22:39:12 PST
Organization: Hewlett-Packard VCD
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>From "The Oregonian," Monday, March 14:
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"A system designed to avert air collisions sent two planes heading 
toward one another near Portland International Airport, and federal 
authorities are trying to figure out why.

"The Feb. 3 incident involved an Alaska Airlines jetliner and a 
HorizonAir commuter jet.

"Each plane was equipped with the Traffic Collision Avoidance 
System, which alerts pilots to other air traffic and sounds an 
alarm if there is a chance of collision.

"'The question is not whehter TCAS did its job.  The question is 
why did the logic of TCAS tell the upper plane to go down and the 
lower plane to climb,' said Dick Meyers, a Federal Aviation 
Administration spokesman based in Renton, Wash.

"A crash would not have resulted if the pilots had continued obeying 
the instructions of the system, but the planes would have come 
uncomfortably close, FAA officials said.

"Alaska Airlines pilot Thomas Hedrick had been instructed by an 
air traffic controller to climb to 9,000 feet and level off.  At 
the same time, a HorizonAir commuter jet piloted by Brian Penwell 
was approaching the airport and was instructed to descend to 10,000 
feet and level off.

"In both planes, the FAA-required collision avoidance system alarm 
sounded -- a common occurence in the traffic-congested skies 
around airports -- letting pilots know they were close to other 
aircraft.

"Then a second alarm sounded indicating the aircraft were on a 
potential collision course.  Rather than advising the pilots to 
level off, the system instructed the higher-flying plane to descend 
below the lower-flying plane and the lower-flying plane to climb 
above the other.

"An air traffic controller noticed the HorizonAir plane descending 
toward the Alaska plane and ordere the pilot to level off.

"'I told him we could not because we were receiving a Resolution 
Advisor,' Penwell wrote in a report filed with the FAA.  A Resolution 
Advisory in this case was the system's directive to descend.

"Penwell said he finally saw the Alaska plane and banked to the left 
at about 9,200 feet.  Penwell estimated that the planes came within 
about a mile of each other."

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Unrelated information:  Alaska Airlines owns HorizonAir.


Richard Nute
Vancouver, Washington, USA