retrieval. In addition to the FDR, many airplanes have
an optional onboard maintenance data system. Maintenance data can
be more easily retrieved from such a system than from the FDR.
One type of onboard maintenance
data system is the airplane condition monitoring system (ACMS) installed
on many 737, 747, 757, 767, and 777 airplanes. ACMS is hosted in
either the data management unit (DMU) or the digital flight data
acquisition unit (DFDAU) on 737, 757, and 767 airplanes and in the
DMU on 747s. It is provided by the airplane information management
system (AIMS) on the 777. Three companies build DFDAUs with ACMS
capability that can be tailored to meet each operator’s unique needs:
Honeywell Aerospace, Redmond, Wash., USA; SFIM, Paris, France; and
Teledyne Technologies, Inc., Los Angeles, Calif., USA.
Bulk flight data from
the ACMS are stored in the quick-access recorder (QAR), located
in the electrical and electronic equipment bay on the airplane.
The QAR operates much like the floppy disk drive on a desktop computer.
It uses a standard optical disk or solid-state memory card as the
storage media. In service, the operator takes the QAR disk from
the airplane and loads the data into a maintenance ground station
computer for further processing.
Because the ACMS is not
required for airplane certification, the operator determines which
information to record. Some operators find the FDR data sufficient
for their maintenance program and put the same data on both the
QAR and the FDR. Other operators specify a different set of parameters
for the QAR for more detailed performance data on systems that tend
to drive maintenance costs such as engines and on operational practices
during landing, takeoff, and taxi.