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The Safety Board is concerned that the procedure of using degrees to set and cross-check
the THS trim setting has resulted in flight crews improperly setting the trim by using a minus (or
UP) value when a plus (or DN) value should have been used. The Safety Board considers pilots
of the two carriers who currently follow this procedure to be at risk for incorrectly setting the
trim as did the pilots on Northwest flight 985 and the April 2000 Lufthansa flight. This
confusion is possible because the degree scale shows some values twice: once to denote pitch up
(“UP”) and once to denote pitch down (“DN”). The CG scale, however, uses a consecutive
series of unique, positive values, which eliminate the opportunity for such confusion.
The Safety Board is also concerned that the revised procedure currently used by
Northwest Airlines to set the trim still calls for the first officer to use the degree scale initially in
setting the trim. Although this procedure makes the captain responsible for catching any mistake
made by the first officer by using a different scale to cross-check the trim setting, this procedure
does not preclude the possibility of mistakes. The Safety Board concludes that a procedure that
uses the CG scale to set and cross-check the trim setting will greatly reduce the potential for
errors that are possible when using the degree scale to set the trim. Therefore, the Safety Board
believes that the FAA should require operators of Airbus Industrie A319, A320, and A321
airplanes to set and cross-check the trim using CG values only.
In addition, the Safety Board is concerned about the inconsistent formats in which trim
unit information is presented to Northwest flight crews and the possibility that other operators
may also use inconsistent formats. As already noted, the degrees scale located next to the THS
trim wheel shows trim values without a “+” or “-” sign, followed by “UP” or “DN” to indicate
the corresponding pitch direction of the airplane. The ECAM also displays trim values to
Northwest flight crews as “UP” or “DN” but also precedes trim values resulting in a nose-up
pitch direction with a “-” sign. Finally, Northwest’s ACARS load data sheet, which is the crew’s
initial source of trim unit information, precedes the trim value with a “-” sign for any setting that
results in a nose-up pitch direction but does not display the corresponding “UP” or “DN”
designations as appear on the trim wheel scale and ECAM display. The Board recognizes that a
6 The CVR indicated that the captain performed the cross-check by stating the trim setting as “negative 1.7.”
5
procedure for setting and cross-checking trim that uses only CG information would not require
flight crews to consult the ECAM or ACARS information regarding the trim setting in degrees.
However, the Board notes that crews may nonetheless choose to consult that information to
confirm that the CG setting selected is consistent with the THS position in degrees. Therefore, to
avoid confusion, the Safety Board believes that the FAA should require operators of Airbus
Industrie A319, A320, and A321 airplanes to ensure that the ECAM display and the ACARS
load data sheet are configured so that they display THS trim unit information in a manner that is
consistent with the display on the degree scale of the trim wheel indicator.
Therefore, the National Transportation Safety Board recommends that the Federal
Aviation Administration:
Require operators of Airbus Industrie A319, A320, and A321 airplanes to set and
cross-check the trim using center of gravity trim values only. (A-02-06)
Require operators of Airbus Industrie A319, A320, and A321 airplanes to ensure
that the electronic centralized aircraft monitoring display and the aircraft
communication addressing and reporting system load data sheet are configured so
that they display trimmable horizontal stabilizer trim unit information in a manner
that is consistent with the display on the degree scale of the trim wheel indicator.
(A-02-07)
Chairman BLAKEY, Vice Chairman CARMODY, and Members HAMMERSCHMIDT,
GOGLIA, and BLACK concurred in these recommendations.
By: Marion C. Blakey
Chairman
AVIATION INVESTIGATION REPORT
A03O0034
RUNWAY EXCURSION
SKYSERVICE AIRLINES INC.
AIRBUS A320-212 C-GJUP
WINDSOR, ONTARIO
11 FEBRUARY 2003
Transportation Safety Board
of Canada
Bureau de la sécurité des transports
du Canada
The Transportation Safety Board of Canada (TSB) investigated this occurrence for the
purpose of advancing transportation safety. It is not the function of the Board to assign fault
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