and incidents related to erroneous flight instrument information
continue to occur despite improvements in system reliability, redundancy,
and technology. In particular, modern flight instruments provide
more information to the flight crew with greater precision. Flight
crews seldom are confronted with instrument problems; however, when
these problems do occur, their rarity can make the situation worse.
To overcome the potential
problems associated with infrequent failures, flight crews should
be aware of the piloting techniques summarized in this article,
follow the guidance described in operations and training manuals,
and comply with airline training when facing a flight instrument
Reviewing the following
important information can help flight crews make the proper decisions when encountering erroneous
flight instrument indications:
erroneous flight instrument incidents.
and static instrument system design.
and recovery techniques.
to assist flight crews.
RECENT ERRONEOUS FLIGHT INSTRUMENT INCIDENTS
Controlling modern airplanes
generally is a routine task in normal and most non-normal situations.
In this era of aural, visual, and tactile warnings and advanced
instrumentation, flight crews consistently are alerted when certain
airplane parameters are exceeded. However, flight crews must react
properly when confronted with instrument failure, which can cause
a significant loss of information. Unfortunately, incidents and
accidents have occurred where flight crews have had difficulty with
erroneous flight instrument indications.
A previous Aero
Flight Instrument Information (Aero no. 8, Oct.
1999), reviewed four accidents and incidents. During the three recent
incidents described here, flight crews were faced with uncertainties
about flight instrumentation.
A Plugged Pitot Probes
An airplane took off with the left and right pitot probes plugged
by insect activity. Primary airspeed indications were inactive during the takeoff roll, but standby airspeed was
normal. The flight crew noticed the condition at an airspeed assumed
to be greater than 80 kias and elected to continue the takeoff.
The captains airspeed
recovered at an altitude between 1,000 and 2,000 ft; the first officers
indicated airspeed remained at 30 kias. The crew performed an air
turnback and a normal landing. The airplane had been on the ground
for 36 hr before the event. The pitot probe blockage had not been
detected during the walk-around conducted by the flight crew.
There have been several
in-service reports of insects such as mud-dauber wasps sealing pitot
probes. These events raise concern about the potential for a takeoff with erroneous
airspeed indications and the possibility of inappropriate crew action,
which could lead to a high-speed rejected takeoff or loss of situational
awareness in flight.
B Open Static Port Drains
An airplane departed without the static port drain caps, which had
been removed during maintenance but not replaced. As a result, the
static lines were open to cabin pressure. There was significant
airframe vibration after takeoff. The flight crew deduced that the
airspeed indicators were under-reading and observed that the altimeter
was not changing. They declared an emergency and returned without
incident. After the flight, maintenance discovered that the flaps
had been damaged by excess speed.
C Partially Blocked Pitot Tube
An airplane departed with the captains pitot tube partially
obstructed by insects. The captains airspeed indication lagged
behind the first officers airspeed indication. The first officer
was conducting the takeoff, and by the time the late callouts and
erroneous indications were identified, the crew decided to continue
During climbout, several
engine indicating and crew alerting system (EICAS) messages were
noted, which later disappeared. Airspeed indications appeared to
be normal. Upon reaching cruise altitude, the captains airspeed
indicated higher than the first officers indication but seemed