Mentor Matters: Circling done right

To answer this question, the pilot should determine if the approach was created under the newest terminal instrument procedures (TERPS) guidance, or if it’s a grandfathered legacy circling procedure. This can be ascertained by the presence or absence of a “C” in either a black box (FAA charts) or diamond (Jeppesen charts) in the circling minimums table. With the “C” present, the procedure was charted under the new TERPS, and the pilot is afforded a comfortable area in which to maneuver. (The FAA began publishing instrument approach procedures that use larger circling approach airspace dimensions in 2013.)

For a light jet flying at Category C speeds, a protected radius of a minimum of 2.7 nautical miles exists, increasing as the minimum descent altitude (MDA) of the approach increases, up to a maximum of 3.3 nautical miles for approaches with an MDA higher than 9,000 feet msl (think Aspen, Colorado). This bump allows an airplane flying at a constant indicated airspeed to still perform a 180-degree turn inside the protected airspace as the turn diameter increases with the true airspeed rise caused by altitude.

Contrast this with the constant 1.7-nautical-mile protected area given to Category C aircraft by legacy procedures. At sea-level airports with low MDAs, maneuvering within 1.7 miles of the runway may not pose a challenge, but at more challenging airports it may make unsafe maneuvers unavoidable.

Consider an Embraer Phenom 300 conducting a circling approach into Aspen. While flying the required circling speed of 130 KIAS at the MDA just over 10,000 feet msl, the true airspeed of the aircraft is 156 knots. With such a high true airspeed, the turn diameter in a 25-degree bank increases from a sea-level value of 1.1 to 1.5 nautical miles. Simply completing the 180-degree turn from downwind to final takes up nearly all of the protected area around the runway; with any tailwind on the base-to-final turn, an overshoot of the centerline is nearly guaranteed.

In some cases, then, legacy circling approaches may simply be deemed an unacceptable risk. In other cases, though, if a circling approach is authorized for Category D aircraft, a pilot can achieve most of the protection afforded under the new TERPS designs by simply electing to fly as if a Category D aircraft. By accepting the (almost always) higher minimums of Category D, the pilot is, in turn, given an extra half-mile to maneuver, with protection extending out to 2.3 nautical miles from the runway.

Once the pilot has settled on the minimums to use, there are several ways to make the procedure more routine. First, it is of the utmost importance that the aircraft be stabilized in the circling configuration, which for most light jets involves a partial flap setting, and at the target circling speed well before the final approach fix. A circling approach is not the time to “hold 180 knots to the marker.” Use of the autopilot is essential as it allows the pilot to focus on energy management rather than diverting attention to basic flying tasks.

Next, it’s important to remember that all circling approaches are nonprecision—even those flown from a precision approach such as an ILS. This means an MDA will be captured, requiring appropriate autopilot mode use. The approach mode, used to track glideslope or glidepath, will not capture MDA, and should not be used.

Rather, descent in vertical speed mode at 1,000 fpm will result in proper capture of MDA and will see the aircraft level at MDA well before the point at which circling can commence. While there is a strong consensus that old-fashioned “dive and drive” nonprecision approaches are unsafe, there is a necessary exception for circling procedures. The sooner the aircraft is at MDA, the earlier the pilot can adjust power to maintain speed and start looking for the airport.

Before reaching the final approach fix, the pilot should have set the heading bug to the heading of the initial turn needed once the airport is visually acquired. This way, once protected airspace is entered, the pilot need only push the heading mode button to begin the maneuver. The heading to which the pilot turns will depend on the angle between the approach course and landing runway, as well as surface winds, and should be determined well before reaching MDA.

The pilot also should set up the multifunction display (MFD) for optimal reference during the circling maneuver. Depending on the flight deck, some or all of the following can be displayed on the MFD: precise range circles around the landing runway to aid the pilot in staying inside protected airspace; an extended centerline to the landing runway to help in planning the base to final turn; and a projected ground track line that will curve while in a turn to show the precise turn radius across the ground. Some information is always displayed (assuming it hasn’t been turned off by the pilot), while other information may require programming the flight management system—again, a task to be accomplished well before commencing the approach.

Once the pilot has commenced the initial maneuvering and is close to starting the turn to base or final, it’s important to have two facts in mind. Having watched hundreds of circling procedures in both simulators and aircraft, I’ve seen that pilots are far more likely to start a turn to final too late than too early. Not only is this error more prevalent, it’s much harder to correct. An early turn to final can simply be shallowed out, while a late turn will involve a centerline overshoot and a frantic attempt to rejoin final from the other side. When in doubt, start turning from base to final early, and make corrections during the turn if needed.

Similarly, if pilots don’t plan their descent from MDA perfectly—and few do—they usually start the descent too late or too shallow, rather than the reverse. Once more, this is harder to correct than an early descent, as descents more than 1,000 fpm are frowned upon when low to the ground. Also, the need to slow the aircraft from circling speed to VREF complicates attempts to quickly lose altitude. Should the pilot recognize an early descent it’s quite easy to add power and shallow it while bleeding off speed, but the reverse can be impossible.

There is one particularly common scenario that causes pilots to roll out on final too high. The pilot begins the turn to final at the appropriate point, announces he or she is leaving MDA, and begins descending. In most airplanes this is also the point at which landing flaps are selected, and if the pilot is overly focused on the turn at the expense of maintaining descent, the ballooning effect of extending flaps will cause the pilot to level off.

This problem is often compounded by an insufficient power reduction when leaving MDA. If the pilot simply pushes the nose down without a large power change, as soon as attention is diverted from the pitch attitude, trim forces will bring the nose right back up to level, foiling the stabilized descent. Just as pilots should start the turn to final as soon as they start to suspect it may be appropriate, they should start and sustain a descent as soon as there’s a hint that the time’s right.

Neil Singer is a Master CFI with more than 9,500 hours in 15 years of flying.