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.")

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.

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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.

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.

FMI: Aero-Tips