As the cost of Global Positioning
System (GPS) units decreases, more pilots are using these devices to supplement
their other navigational equipment. However, problems can arise when some
pilots fail to recognize that GPS is designed to be a supplemental --
not a primary-navigational aid. A report from a corporate pilot illustrates:
- I departed
on an IFR flight plan with an IFR-approved GPS. I was cleared direct
to ABC, at which time I dialed ABC into the VOR portion of the GPS and
punched "direct." The heading was 040 degrees. After a few
minutes, Approach inquired as to my routing, heading, etc. I stated
direct ABC, 040 degrees. They suggested turning to 340 degrees for ABC.
I was dumbfounded. My GPS receiver had locked to ADC, 3,500 miles away
[in Norway]! Closer inspection revealed that my estimated time en route
was 21 hours.
I did not verify my position with the VOR receiver. I mistakenly, blindly,
trusted a GPS.
Now that is truly global
Other reporters have found
themselves somewhere other than where they wanted to be as a result of
overreliance on GPS. A general aviation pilot provides an example:
- I recently
purchased a hand-held GPS, and was anxious to use my new acquisition.
Without thinking (obviously!), I punched in XYZ VOR and navigated along
the direct route. I did not cross-check myself with the VORs and allowed
myself to invade restricted airspace. I tuned in 121.5, and received
instructions and polite guidance out of my dilemma. I realize that this
is a serious problem and a very stupid mistake.
Many hand-held GPS units have
an inherent system limitation, as our next reporter discovered.
- Flying VFR,
using a hand-held GPS for navigational reference. While en route, position
and status seemed fine. According to the GPS position, a "big airport"
was getting closer and closer, but still out of the overlying Class
C airspace. From a visual standpoint, the position was definitely in
Class C airspace. When I landed at ABC, the GPS indicated the location
was XYZ [about 40 nm west]. I turned the unit off, then back on, and
the position now indicated ABC.
I called the manufacturer, which had received numerous calls about erroneous
positions. A new satellite had been put in orbit; there were now a total
of 26 satellites. My unit only showed 25. The manufacturer suggested
leaving the GPS on for 45 minutes to acquire the information from the
new satellite. I did so, and my unit now shows 26 satellites. The GPS
positions seem correct.
Conclusion: use hand-held GPS as a reference only.
According to the reporter's
conversation with the manufacturer, hand-held GPS units currently in use
do not have the RAIM -- Receiver Autonomous Integrity Monitor -- that
is built into installed, IFR-certified units. The RAIM monitors the actual
navaid signal, primarily on SID and STAR routes, to assure that there
is adequate signal strength for navigation in the selected mode. If the
signal is not sufficient, an error message will occur. This is analogous
to the 'OFF' flag showing on the VOR receiver when the aircraft is out
of range for adequate signal acquisition. Since the reporter's GPS unit
did not have RAIM capability, there was no way to know that the unit was
providing erroneous information.
Because of the inherent limitations
of hand-held units, pilots should carry and use the appropriate charts
as cross-reference material, rather than relying solely on GPS.
When properly programmed and
used, GPS has incredibly accurate position reporting capability, which
can prove to be a lifesaver -- literally. The next reporter, the pilot
of a long-range amphibious airplane on a ferry flight across the Pacific
Ocean, tells a "GPS-to-the-rescue" story.
- While we
were ferrying the aircraft...the left engine began backfiring severely
and would not develop [power]. Engine #2 was brought to METO [Maximum
Except Take-Off] power attempting to maintain best altitude. An immediate
turn was made for the nearest land, and our "Pan" emergency
shifted to a "Mayday" call.
After about one hour, descent into the water was imminent. The night
ocean visibility would be termed zero/zero...and a standard night IFR
approach was set up. After a successful night IFR water landing, we
began taking on water. Seven people escaped without injury into a lifeboat.
Coordination with ATC and very accurate position reporting with GPS
resulted in a very expeditious rescue by the Coast Guard and a maritime
vessel. We were in the ocean less than one day. Very spectacular efforts
by all parties involved.
Good pre-flight planning is
particularly important when flying an aircraft with special needs -- like
an appropriate landing surface, in the case of a floatplane. Our first
reporter, en route to the national airshow in Oshkosh, Wisconsin, apparently
hadn't fully planned for fuel:
- I was on
my way to Oshkosh, flying my floatplane and looking for a fuel stop,
as I was getting low on fuel. Cruise altitude was approximately 800
feet AGL, but I went lower to look for fuel pumps at likely docks. I
found a marina on the lake and fueled up, then continued on my way.
There are very few seaplane bases, so finding fuel stops is difficult.
Although sectional charts may
not always indicate the presence of seaplane bases, national or local
seaplane associations, and some airport guidebooks, have listings for
seaplane facilities. Additional prior planning might also have saved the
reporter from a possible violation of the FARs concerning minimum safe
- I was going
to perform helicopter water bucket drops for the crowd. The helicopter
was on display and open to the public, so I was expecting the switches
to be in the wrong positions. I performed a thorough pre-flight of the
cabin, however I did not think to check the cargo hook release [on the
belly of the aircraft], which apparently had been tripped. During the
demonstration, the bucket came off the aircraft at 200 feet AGL, and
landed on the taxiway. There were no injuries. This could have been
prevented if I had checked the hook release prior to departure.
A pre-flight check of all equipment
is particularly important after an aircraft has been made accessible to
an interested public.
Even for an experienced pilot,
encountering wake turbulence at very low altitude and at racing speeds
can be startling at the very least, and at worst, downright disastrous.
- During a
biplane race, I encountered strong vortices from another aircraft. While
recovering, with other aircraft above me, I inadvertently may have gone
below the height of the top of the pylon. The officials at the pylon
reported a low pass-by. While some turbulence had been anticipated,
the turbulence was much stronger than encountered previously. A real
This reporter is indeed fortunate
that the only consequence of this incident was to catch the attention
of race officials.
- We were
making our last fuel stop for the day after leaving a fly-in. Since
our aircraft had no radio, we noted the wind direction from the wind
sock. The only visible traffic was taxiing out for take-off. We landed
after his departure and were taxiing to the fuel pump, when what I thought
was an overzealous line boy stopped us and demanded we shut down. I
told him all we wanted to do was get gas and be on our way. He told
me that we were not going anywhere and to get out of the aircraft. He
said the field was closed as an airshow was in progress. At this point,
I saw his FAA identification badge.
He and his partner checked all our paperwork and allowed us to gas up.
The airshow waiver time was over in about 20 minutes...we took off behind
5 other departing aircraft.
Checking NOTAMs for the route
of flight and airports of intended landing would have provided the information
the pilot needed to avoid this encounter.
Officer (FO) was the flying pilot as we executed the ILS approach.
At approximately 25 feet prior to decision height, I announced,
"I've got the runway." The FO apparently did not hear
my callout correctly, and misinterpreted it as a request that he
relinquish the controls to me. He replied, "OK, you've got
it." I immediately responded, "No, no -- you've got it."
During this exchange, the aircraft began to drift to the right of
the centerline. It became apparent that there was still confusion
as to who would manipulate the controls for landing. As such, I
took control of the aircraft and...accomplished a normal landing.
post-flight discussion, we agreed that phraseology was the primary
factor which led to our miscommunication. Non-descript terminology
such as "I've got it/You've got it" left open the possibility
for misinterpretation as to whether the speaker was referring to
the runway or the aircraft.
Recently Issued Alerts On...
failures in an MD-80 and an MD-88
jumping activity near a Nevada arrival route
computerized groundspeeds at a Utah Center
engine reversal due to propeller governor failure
and elevator trim malfunctions on a Beech King Air
1997 Report Intake