In
recent years, handheld Global Positioning System (GPS) units have become
more affordable and more widely used. Many General Aviation (GA) pilots,
in particular, find handheld GPS units a convenient supplement to other
navigation methods. Mechanical problems with GPS are infrequent; a more
common problem reported to ASRS is that old bogy—operator error.
A GA reporter illustrates:
- I descended
through a hole in the broken layer thinking I was 5 statute miles
from [the airport] based on my GPS and DME. It appears I might have
been inside the airport’s Class D airspace. Trying to familiarize
oneself with a new handheld moving map GPS while flying in a broken
cloud layer environment and cross-checking with VORs and GPS is not
a bright thing to do. Next time, it will be in severe clear and with
a second pilot onboard.
Our reporter offers good
advice for future GPS familiarization flights. Another GA pilot relied
only on the GPS to maintain positional awareness, and found the information
deceiving:
- While watching
my progress on the GPS moving map, at approximately one mile from
XYZ intersection, it appeared I would be clear of the Class B airspace
by the time I reached 3,000 feet. [However] I reached 3,000 feet prior
to clearing Class B, and was informed to remain clear by ATC. I believe
the automatically-sequenced map scale was a contributing factor, as
it was set on a high mileage scale, which compressed the locations
of XYZ intersection, the Class B airspace, and my position.
Appropriate cross-checking
with other navigational aids might also have prevented this pilot’s
unauthorized penetration of Class B airspace.
In an effort
to get back to his home base, our next reporter passed up a perfectly
good VFR airport en route, and then the problems really started to pile
up:
- Halfway [to
my destination], the GPS batteries failed, ceiling and visibility
lowered, I lost radio contact with Approach because of my low altitude,
and was unsure of my position. I finally found [my destination] by
dead reckoning. I made a poor decision not to land at [an intermediate
point], where I could have plotted a course by VOR navigation and
changed GPS batteries which I knew were low.
Never fully depend on handheld GPS for position, and keep fresh batteries
installed.
In
spite of what some passengers may believe, the cabin crew’s primary
duty is to ensure passenger safety. This duty becomes obvious during an
aircraft emergency, when the crew’s skills and training come to the
fore, as described in this report to ASRS on an emergency descent and
landing:
- I was seated
in the aft part of the aircraft and I noticed some unusual changes
in cabin temperature and airflow. Another Flight Attendant came to
the back and said that she had been in the cockpit and the pilots
seemed to be having some problem. I could tell we were descending.
About this time, the Captain made a PA [Public Address] announcement
stating that we were having a pressurization problem and that we might
have to use the oxygen masks. He also asked passengers to make sure
their seatbelts were fastened. I made my way to the front, checking
seatbelt compliance. At this point, we seemed to be descending rapidly...[and]
the oxygen masks deployed throughout the aircraft. I donned a mask...and
slowly worked my way to the back, checking on passengers. All passengers
seemed to get their masks on with no problems. The Lead Flight Attendant
made the required PA announcement per our procedures. Our Flight Attendant
procedures seemed to work well.
Flight Attendants receive
extensive initial and recurrent safety training just so that all emergency
procedures go as smoothly as the ones in this incident did.
Next, cool heads and good
crew communications combined to bring an emergency return-to-land incident
to a textbook conclusion, as described in this report from a Flight
Attendant:
- On takeoff
roll, multiple loud thumps (explosions) were heard when the left gear
inside tire blew and made an incision into the wing, then entered
the engine. We contacted the Captain and gave him as much information
as possible. He informed us were going to return to make an emergency
landing, and we did so without incident.
Since the cabin crew provided
the Captain with a thorough assessment of the damage, none of the flight
crew needed to leave the cockpit to survey the damage personally. All
three flight crew members were able to remain in the cockpit and concentrate
on preparing for the emergency landing.
U.S.
Air Traffic controllers generally avoid attaching conditions to their
taxi instructions. However, "conditional clearances," in which
the pilot’s compliance with an instruction is dependent on the completion
of an action by an arriving or departing aircraft, are common at many
foreign airports. A pilot’s lack of familiarity with conditional
clearances can lead to runway transgressions and other problems, as evidenced
by this report to ASRS from a military transport pilot flying in a foreign
country.
- The clearance
as we perceived it was "cleared onto the runway to wait following
air carrier X" (air carrier X being the one that was beginning
its takeoff roll). Traffic on a 5-8 mile final was observed, but the
thought was that we would receive an immediate takeoff and we read
back the clearance as we heard it. Upon seeing the aircraft in front
commence his departure turn, we queried Tower for takeoff clearance.
At that time, he informed us that we had been "cleared [onto
the runway] following the landing traffic." He sent the landing
traffic around.
We are not accustomed to the...conditional clearance and had not given
forethought to the hazards involved.
In another incident at a
foreign airport, the First Officer of a widebody jet reported a similar
misunderstanding of a controller’s conditional clearance.
- We were holding
short of the runway. Two other heavy jets had just taken off with
very tight departure spacing. As soon as the jet before us was airborne,
both my Captain and I understood the Tower Controller to say, "Traffic
on a 3-1/2 mile final, line up Runway 8." I specifically read
back: "Cleared to line up Runway 8," with no mention of
a conditional clearance. I looked again and saw the final approach
traffic about three miles out. I thought there was ample spacing for
our takeoff between the departing and arriving traffic, and expected
Tower to clear us for takeoff as we taxied into position. About one
minute later, the Tower told the aircraft on final approach to go
around, and told us that he had cleared us to line up on Runway 8
after the final approach traffic had landed.
A final report illustrates
how a conditional clearance can be implied in the phraseology of a controller.
- We were cleared
by the Tower, "Line up and wait, air carrier Y on three mile
final." We responded, "Roger, line up and wait." We
taxied into position and hold, at which time we noticed the jet on
final. Tower then instructed air carrier Y to go around. Tower told
us after the go-around that he had told us, "Line up and wait,
after the air carrier on a three mile final."
Unless the specific conditions
of a clearance are explicit and unambiguous, pilots need to query the
controller for clarification or for additional information as soon as
possible following issuance of the clearance.
The
Captain of a DeHaviland Dash 8 on approach into an East Coast airport
reports a different sort of "conditional clearance":
- We had briefed
for the ILS approach. We were tracking inbound on the localizer and
Approach Control kept us high (above glideslope) before clearance
for the approach. I elected to fly the approach manually to facilitate
intercepting the glideslope from above. We contacted the Tower at
the Final Approach Fix [FAF]. Not long after the FAF, I heard the
Tower issue a caution to the aircraft ahead of us that there was a
ship in the channel with a height of 150 feet. The Tower Controller
then issued the same "Caution, ship in channel, 150 feet in height"
to us. At this point we were over halfway between the FAF and the
runway. While concentrating on flying the approach, in the back of
my mind I was trying to consider the significance of the caution.
We continued the approach and made contact with the approach lights
just above the normal decision altitude [DA] (218 feet). After landing...we
looked over the approach chart and realized the "conditional
DA" [359 feet] for tall vessels may have applied. I did not know
what height constitutes a "tall vessel." It is not written
anywhere that I could find. I asked Clearance Delivery and they did
not know, but they checked and told us it was 85 feet or higher. Oops!
We were clearly remiss in not catching the "conditional"
DA during the briefing, but there were several issues that "set
the trap" for us. First, there was no mention of ships in the
channel until we were well inside the FAF. Second, the Controller
did not use the terminology "tall vessels," which gave us
an ambiguous caution message.
The reporter recommends that
ATC use the phraseology, "Tall vessels in approach area,"
which is the wording found on both NOS and commercial approach plates.
This terminology would likely have triggered recognition among the flight
crew that the higher, "conditional" decision altitude was
required.
