AD Addresses Potential Altitude Error in L-3 TAWS

 - March 22, 2007, 8:21 AM
An AD for the Landmark 8000 terrain awareness and warning system (TAWS), manufactured by L-3 Communications Avionics Systems, corrects potential altitude errors. Technicians uncovered the problem after connecting a Landmark TAWS to the baro set voltage divider in a Citation 500 through its Honeywell BA-141 altimeter and AZ-241 air-data computer. According to the FAA, the altimeter in this installation showed the airplane to be 60 feet higher than the actual altitude. Laboratory testing subsequently confirmed that altimeters will show incorrect altitudes when connected to the same baro set potentiometer as the Landmark TAWS. The AD affects about 80 airplanes and requires about an hour of labor to check the installations and make modifications. The FAA said that L-3 has since incorporated a production upgrade in the Landmark TAWS that eliminates the problem in new units.