Filtered Flight Data, Final Rule
effective April 20, 2010 for 14 CFR Parts 121.346,
125.228 and 135.156
The Federal
Aviation Administration (FAA) amended the flight data
recorder regulations affecting air carriers and
operators. The new rule prohibits the filtering of some
flight recorder sensor signals unless the data can be
accurately reconstructed.
The NTSB and FAA found that some digital flight data recorder
(DFDR) systems are filtering sensor signals before being
recorded. As a result, the recorded data may not
accurately reflect the aircraft's performance or the
movements of the flight control systems.
The FAA rule requires that operating certificate holders
identify which (if any) DFDR parameters are being
filtered. The parameters that must be evaluated are
flight control surface positions, flight control input
positions, flight control forces, and throttle lever
position. The system information may be acquired from
the equipment manufacturer and physical system tests may
not be necessary.
The FAA stated that a flight data recorder signal is
considered filtered when an original sensor signal is
changed in any way, other than changes necessary to:
(1) Accomplish analog to digital conversion of the
signal,
(2) Format a digital signal into a DFDR compatible
format; or
(3) Eliminate a high frequency component of a signal
that is outside the operational bandwidth of the sensor.
The rule requires that, for the flight control related
parameters, the aircraft DFDR system either (1) record
unfiltered data, (2) record filtered data that meet the
required accuracy specifications, or (3) record filtered
data that can be reconstructed to recover the original
unfiltered sensor signal values. So long as the
applicable appendix requirements are met, this rule
allows the operator to select the lowest cost compliance
alternative.
If filtering is found on the applicable parameters the
certificate holder must determine if the recorded data
meets accuracy requirements. If they do not, the
operator needs to decide whether to attempt data
reconstruction or alter the DFDR system to record
unfiltered data.
Operators have until October 20, 2011 to review their
DFDR systems and create a record that indicates whether
the DFDR system on each airplane is filtering any of the
parameters included in the “no filter list.” If no
parameters are being filtered, that record entry should
be made at the time of the determination, and an
operator need take no further action unless a change is
made to a DFDR system. A record of each airplane's
status regarding filtering is to be maintained as part
of the flight data recorder correlation documentation.
Operators that identify filtered parameters will have
two options. If an operator chooses to remove the
filtering, it has until April 21, 2014 to make the
system modifications. If an operator chooses to
demonstrate by tests and analyses that filtered data can
be reconstructed, the operator has until April 22, 2013
to submit its reconstruction package to the FAA for
approval.
L2 has the
DFDR test/readout equipment for just about every DFDR
currently in operation along with well trained and
qualified DFDR technicians and AOG teams that specialize
in downloading and reviewing the data to ensure it is
valid.
L2 can assist
operators to understand and meet DFDR FARs by the FAA
deadlines.
FAA guidance will be included in Advisory Circular
20-141B “Airworthiness and Operational Approval of
Digital Flight Data Recorder Systems.”
Please contact
L2info@L2Aviation.com to schedule a review of your
DFDR system or if you would like more information.
