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The reported the anomalous behavior is
consistent with significant water ingestion or
simultaneous icing of two or three of the three
pitot probes. The FAA has received three reports
of in-service displayed airspeed anomalies on
Model 787 airplanes. During each of the reported
events, the displayed airspeed rapidly dropped
significantly below the actual airplane
airspeed. In normal operations, the air data
reference system supplies the same airspeed to
both the captain and first officer primary
flight displays.
During one in-service event, with autopilot
engaged, the pilot overrode the engaged
autopilot in response to the displayed erroneous
low airspeed and made significant nose-down
manual control inputs. In this situation, there
is the potential for large pilot control inputs
at high actual airspeed, which could cause the
airplane to exceed its structural capability.
The FAA is issuing this AD because they have
evaluated all the relevant information and
determined the unsafe condition described is
likely to exist or develop in other aircraft of
the same type design. The FAA will continue
to investigate this issue with Boeing.
This AD requires revising the AFM to add a
''Non-normal Procedure'' for ''Airspeed Drop''
that instructs the flight crew to avoid abrupt
flight control inputs, and reinforces the need
to disconnect the autopilot prior to making any
manual flight control inputs.
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