3 / 5
DOT N°:38 dated Feb 25/2008 © Société Air France 2002 - All rights reserved
TITLE: Treatment of the incidents with loss of the airspeed indication
REFERENCE : SIL 34-084
Link with AIRMAN (WRN/FLR)
YES / NO
E F F E C T I V I TY
AFR X THT
X KLM X
The purpose of this NT is to gather information in order to confirm the involvement of pitot probes in
case of “Nav IAS discrepancy”.
At the time of creation of the NT, a case on THT and six cases on A340 AFR have been reported.
Investigations conducted on Airbus family aircraft showed that most of airspeed discrepancy events
were due to Pitot water ingress and to probe draining holes obstructed by external particles.
Another hypothesis is in study on a possible saturation of pitots by crystallized ice in high flight level.
In particular flight condition, a speed discrepancy between system 1 and 2 or total loss of airspeed
indications could appear with auto pilot disengagement, auto thr off, etc…
-F/CTL ALTN LAW
-WINDSHEAR DETECT FAULT
-NAV IAS DISCREPANCY
-AUTO FLT AP OFF
-AUTO FLT A/THR OFF
These characteristics warning appeared simultaneously, the auto pilot disengagement occur when
system 1 and 2 lose their information.
In order to confirm the pitot fault it is necessary to perform the maintenance actions below.
These procedures are to be performed in the order described below,:
Make a copy of the form found in the annex. If the crew is always on board, ask them
to complete the first two parts of the questionnaire, and fill the "post-flight check result" after
performing the actions below. Forward this information to the eng. Fonda ATA 34.
Inspection check of the pitot probes: AMM 34-11-15-200-801, pay attention to