Number 1 : March 1991
by Mike Smiley
Recently an incident was reported
to ASRS that emphasizes the need for flight crews flying advanced technology
aircraft to back up the computer-generated route and navigation database with
"old fashioned" navigation charts. Let's examine this incident through
the eyes of the reporting flight crew:
- "We were in the approach
portion of the flight, among scattered cumulus clouds and thunderstorms, on
autopi lot with LNAV and VNAV engaged. We had been told to expect no delays.
Approach Control gave traffic ahead holding instructions at [intersection
A] with right turns instead of the published left turns because of a thunderstorm.
We verified the cell on our radar and received holding instructions, also
at [intersection A] with right turns. When we were about 20 miles from [intersection
A], Approach Control issued clearance for us to hold at [intersection B] because
of weather. We tried to enter [intersection B] as a waypoint but the computer
rejected it as 'not in NAV DATA BASE.' By the time we located the distance
from the VOR to [intersection B] on our charts and switched to VOR mode we
were past the intersection. The controller asked us if we knew we were 5 miles
past [intersection B] and issued a heading. We complied and shortly after
were vectored inbound."
A rare occurrence? An isolated event?
Not at all! You can find related incidents in the ASRS database spanning many
years and involving virtually every phase of flight.
Phase of Flight
- "After receiving clearance,
a departure route was programmed into the FMS. Ground Control asked if we
would accept Runway 01, but we declined due to crosswind and requested Runway
28. I changed the runway in the FMS but in the process of programming, I did
not activate the revised departure route. The result was that no course line
was displayed from the runway to the first fix. Confusion and lack of communication
between the captain and myself led to our lack of 'a last minute' verification
of charts and specific departure procedures. After takeoff, the Captain initiated
what he thought was the correct turn. Departure Control soon asked us if we
were flying the revised departure route. We replied 'Negative.' "
The flight crew sums it up--"Problems
of this type can only be avoided through greater vigilance and a commitment
to use whatever caution necessary to avoid such errors; one must avoid undue
dependency on computer generated flight paths."
The enroute phase is the phase of
flight where technology has supposedly all but eliminated workload. Or has it?
- "The controller instructed
us to hold at [intersection B] on the airway, left turns, 10 mile legs. I
inadvertently started to hold at [intersection A] and ATC told us to turn
right immediately to a 090 degree heading. He then cleared us direct to [intersection
B] to hold on the airway...." The crew suggests complicating factors,
among them "relying on the database without maps available."
Descent and crossing fixes add their
share to the dilemma:
- "We were issued clearance
to cross 50 [miles] north of the VOR at [FL] 270. I punched it into the FMS
using a new waypoint I thought was 47 north of the VOR. However the aircraft
had not begun descent when ATC asked us how far north of the VOR we showed.
As the VOR receivers tune automatically, it took a few moments to find a chart
and obtain the VOR frequency--whereupon we discovered we had just passed the
50 mile fix."
Even the approach phase is not immune
from track errors, although this is usually where the crew is very alert:
- "The FMC was working slowly
and incorrectly. We set up the computer for the ILS approach and received
vectors from ATC. I thought the vectors were for the ILS but they were really
for the VOR approach to a visual. Tower then said we were too high, and, if
the field was in sight that we were cleared for a visual approach."
Sometimes re-programming woes appear
to be caused by a combination of ATC not understanding flight crew workload,
and the flight crew not being ready for changes. ATC clearance amendments that
are not on the FMC route of flight can pose significant workload increases for
flight crews flying advanced technology aircraft, even when the flight crew
is able to comply. If the clearance change is received when the workload is
already high, such as immediately prior to takeoff, the result can be even more
- "Tower said '...cleared for
takeoff, maintain 2000 feet, at [VOR] 154 degree radial turn left heading
220 degrees.' We had to sit on the runway, pull out different maps, install
the 154 degree radial, locate the [VOR] identifier and reset clearance altitude."
As we all know, today's ATC environment
is getting more congested and complex. Advanced technology aircraft systems,
though reliable, are not perfect and will occasionally malfunction. A sure
defense against this condition is to have all appropriate charts available.
Additionally, if any difficulty is encountered in programming or utilizing
automated flight management systems, don't hesitate to take manual control of
the aircraft and fly it where you are supposed to go. Implement these two
simple rules and you will avoid, "...at least I thought I was there."
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