Articles, Training

Are You Stable?

Posted on Feb 1, 2021 by Bill Frank

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On July 31, 2015, a Phenom 300 with a pilot and three passengers was attempting to land at Blackbushe Airport outside of London, England. The aircraft ran off the far end of the runway, struck an earthen embankment and became airborne again before colliding with cars parked in an adjacent lot. The subsequent accident investigation revealed a highly unstable approach in VFR conditions. The pilot was descending on final at 3,000 fpm and crossed the runway threshold at 151 knots, 40 percent faster than the Vref of 108 knots. This was a pilot fixated on landing. The first point of touchdown was three quarters of the way down the length of the runway, at which point the outcome was no longer in doubt. All aboard died in the crash.

Several years ago, following a rash of Cirrus landing accidents I wrote a set of articles in the COPA magazine titled “Landing a Cirrus – The Good, The Bad and the Ugly.” The two-part article focused on the mechanics of landing, beginning with the base-to-final turn through rollout and a possible go-around. Cirrus Aircraft sent an open letter to all current owners of Cirrus airplanes encouraging more landing practice and training which, shortly thereafter, led to the development of the Landing Standardization syllabus. I promised a follow-on article discussing flying a stabilized approach, as the saying goes, “A good landing follows a good approach.” Cirrus has incorporated the criteria for stabilized approaches in the iFOM and this will be the focus of the following discussion.

Stabilized Criteria – VFR Approach

  • Proper Airspeed: I can’t express strongly enough how critical the element of airspeed control is. Final approach speed or Vref for your Cirrus aircraft should be memorized and can be found in the iFOM. That speed references gross weight, so at less than gross weight Vref can be reduced (roughly) by one knot for every 100 pounds below gross weight (or more conservatively one knot per 200 pounds below gross). Most every Cirrus landing accident has involved poor airspeed control.
  • Correct Flight Path: If you rollout from the base-tofinal turn well off of the runway centerline, the time to go-around is NOW! Too many pilots have paid a heavy price trying to fix that error on an approach. Know where the wind is coming from and make appropriate adjustments on the downwind leg.
  • Correct Aircraft Configuration for Phase of Flight: All landings in a Cirrus, in visual conditions, are completed with full flaps set on the base leg. A no-flap landing is an abnormal procedure and requires adjusting Vref by +10 knots.
  • Appropriate Power Setting for Configuration: 50 percent flaps add significant lift with only limited drag; full flaps are mostly all drag. Be prepared to adjust power settings accordingly. Dragging in an approach with full flaps and a high power setting is likely to result in a botched landing.
  • Normal Angle and Rate of Descent: As an instructor, the most common error that I see is pilots trying to salvage an unstable approach, which demands an immediate go-around. It’s okay to make minor adjustments in glide path and sink rate (see next point), and pilots do this routinely while hand flying an ILS.
  • Only minor corrections are required to correct for deviations: Small fluctuations in airspeed and descent rate can be expected, as long as they are acknowledged and prompt corrective action is taken, the approach may be continued.

ALL of these criteria must be met by 500 feet AGL or a go-around is mandated. If your superior flying skills couldn’t meet the above criteria, those skills are not likely to salvage the approach so take the go-around and try again. No penalty is applied.

Stabilized Criteria – IFR Approach

These criteria must be met at 1,000 feet AGL:

  • Proper Speed: Cirrus pilots should know Pitch/ Power/Configurations to obtain proper airspeeds during the approach. Again, these are detailed in the iFOM for the various models of Cirrus aircraft. The speeds are standardized to be 120 knots from the IAF to Glideslope/Glidepath alive for approaches with vertical guidance, and 2 miles from the FAF for approaches without vertical guidance. Once inside the FAF, speed is standardized to 100 knots. As an aside, the same power setting that gave you 120 knots with no flaps, will give you ~100 knots with 50 percent flaps once leveled off at MDA. So, on an approach you only have two power settings to deal with.
  • Correct Flightpath: Hand flying with or without the flight director, a proficient pilot should be able to maintain course and vertical guidance within a half-scale deflection; beyond that the approach is not stabilized and a missed approach should be initiated. Do not let things go to a full-scale deflection before taking action, this is dangerous with diminishing obstacle clearances. If coupled, and you notice the Glideslope/Glidepath moving quickly beneath you, you most likely forgot to select Approach Mode (APR) on the autopilot. If you catch your mistake early you can descend in VS mode to intercept the GS/GP from above, but do so at rates that do not exceed 1,000 fpm.
  • Correct Aircraft Configuration for phase of flight: Cirrus recommends 50 percent flaps on descent inside of the FAF. A more recent recommendation is for no further configuration changes if breaking out of the clouds below 500 feet AGL. Continue in that configuration to landing, adding 5 knots to Vref. Plan ahead for adequate runway length and consider runway contamination.
  • Appropriate power settings for aircraft configuration: Again, these are spelled out in the iFOM for different Cirrus models and work out extremely well. Standardize yourself to these power settings.
  • Normal angle and rate of descent: Limit rate of descent to 1,000 fpm maximum, and you should normally be at a rate of no more than 600 fpm on a precision approach and 800 fpm on a nonprecision approach.
  • Only Minor Corrections are Necessary to Correct Airspeed, Glidepath and Lateral Deviations: On both ILS and LPV approaches, sensitivity increases the closer you get to the runway; try to bracket heading changes to 5 degrees and pitch changes to 3 degrees. If using the flight director, keep the V bar tight under the Command Bar. In the same manner make small changes in power, bracketing in 5 percent increments, and allow time for the energy state of the aircraft to catch up.

Conclusions:

Flying a stabilized approach to landing, whether in the traffic pattern or an instrument approach, will allow the greatest chance of a successful landing. Recognizing when the approach becomes unstable is critical to decision making and is where many pilots become fixated on salvaging the approach. Often these attempts are successful, creating a cache of negative learning. Pilots, particularly professional pilots, are often embarrassed to execute a go-around, fearing criticism from their company and their peers. Fortunately, that attitude is changing, and go-arounds from unstable approaches are being encouraged. We Cirrus pilots, flying technically advanced, high-performance aircraft should push ourselves to make an early decision to perform a go-around when we can’t meet the above criteria. It’s a responsibility to ourselves, our passengers, and those on the ground to standardize our flying and strive to constantly improve our skills.


This article was initially published in the July / August 2019 issue of COPA Pilot.

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