Aero-Tips!
A good pilot is always learning -- how many times have you
heard this old standard throughout your flying career? There is no
truer statement in all of flying (well, with the possible exception
of "there are no old, bold pilots.")
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Aero-News has called upon the expertise of Thomas P. Turner,
master CFI and all-around-good-guy, to bring our readers -- and us
-- daily tips to improve our skills as aviators. Some of them, you
may have heard before... but for each of us, there will also be
something we might never have considered before, or something that
didn't "stick" the way it should have the first time we memorized
it for the practical test.
Look for our daily Aero-Tips segments, coming each day to
you through the Aero-News Network.
Aero-Tips 07.12.06
Remember the four T's* (or the five T's**, or the six T's***)?
They're a staple of instrument instruction, a quick reminder of
tasks that may need done passing a fix or entering a hold or
crossing the Final Approach Fix (FAF) inbound. Losing ground
rapidly in this era of GPS and moving maps, the T's contain one
item that was absolutely critical as little as a decade ago, and
which still has great value today-the time you cross a fix.
Notes:
- * Turn, Time, Twist (or tune), Talk
- ** Turn, Time, Twist, Throttle, Talk (adds "Throttle" for power
changes as necessary)
- ***Turn, Time, Twist, Tires, Throttle, Talk (adds "Tires" to
extend retractable gear)
Approach timing
Until little more than a decade ago, when IFR LORAN and later
GPS revolutionized IFR navigation, almost all nonprecison
approaches included a Missed Approach Point (MAP) that was
determined by estimating your ground speed inbound on the approach,
and flying a length of time until your estimated ground speed put
you over the MAP. It sounds horribly imprecise today, but it was
state-of-the-art and it worked.
Instrument approach procedures include a box listing the times
from the FAF to the MAP at various ground speeds. Since the
distance from FAF to MAP varies widely from runway to runway, the
times can be different for every approach.
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Exceptions:
- If the VOR or NDB used for the approach is on the airport, the
MAP is usually defined as the point where you note station passage.
In this case the "time boxes" are empty because there is no
depicted FAF and different procedures apply.
- Sometimes the MAP could also be defined by crossing radials or
bearings from off-approach VORs or NDBs. The accuracy of
cross-bearings depends on distance from the off-approach beacon, so
timing is still important to help define the MAP.
- Distance Measuring Equipment (DME) is far more accurate than
timing, so DME-equipped airplanes on DME approaches use DME in lieu
of timing.
- GPS approaches, which define the MAP with a waypoint, do not
contain the timing information box.
It's the pilot's job in a timed approach to guesstimate ground
speed based on known airspeed and available information on headwind
component flying inbound. This seems archaic (and in a GPS world,
it is), given the variable winds with changes in altitude and the
sometimes dubious accuracy of surface wind reports at outlying
airports. But the system works if a pilot makes an honest effort
and holds a constant airspeed during the approach.
Timing on ILS approaches
Why compute and track time from FAF to MAP on an ILS approach
(where altitude determines the MAP)? Simple: it's a great
cross-check. It's not uncommon to mis-read an altimeter in the heat
of battle. Thinking you're higher than you are, or forgetting
decision height and following the glideslope into the ground,
appears to be a factor in many IFR mishaps. Cross-checking with
time gives you one more prompt that you are approaching the MAP
Aero-tip of the day: Start a timer crossing the
FAF inbound…it may be your only means of identifying the
MAP, and even on an ILS it provides a vital safety cross-check.