Setting Stabilized Approach Criteria

A couple of weeks after the Asiana accident, the FAA's General Aviation Joint Steering Committee selected stabilized approaches as its Safety Enhancement Topic and put out a notice stating, in part, "...if something's not right, at any time, GO AROUND! There's no shame in going back up to take another shot at it."

Runway 28L at San Francisco is 11,381 feet long with a 300-foot displaced threshold and an elevation of 12.7 feet MSL. According to briefings by NTSB chairman Deborah A. P. Hersman, the flying pilot told investigators that when they were at 500 feet MSL, he saw three red lights and one white light on the precision approach path indicator (PAPI), meaning they were low on the approach path. He also said there was a flash of light from an unknown source, possibly a reflection of the sun, but it didn't interfere with his vision.

Information gathered from the cockpit voice and flight data recorders indicated there were elements in addition to the PAPI display, which should have alerted the flight crew that their approach was unstabilized and they needed to take action much sooner than they ultimately did.

The airplane's Vref speed for the approach was 137 knots. At 1,000 feet MSL, 54 seconds before impact, the airspeed was 149 knots. At 34 seconds prior to impact, when the airplane was down to 500 feet, the airspeed was already below Vref at 134 knots. At 200 feet, 16 seconds before impact, the airspeed was down to 118 knots.

At eight seconds before impact, at 125 feet, the engine throttles started moving forward, and the airspeed was 112 knots. At four seconds before impact, the stall warning stick shaker activated. Just three seconds before impact, there was a call for a go-around as the engine power rose to about 50% and the speed was down at 103 knots. At 1.5 seconds before impact, a different crewmember made a second call for a go-around. But, it was way too late.

One airline's criteria for determining when an approach is stabilized included the glide path being no more than one dot off the center of the glideslope and/or localizer, speed no more than 10 knots above the appropriate threshold speed, zero knots below the desired speed, and having a maximum descent rate of 900 feet per minute between 300 feet and 59 feet AGL.

Because they're generally not working in the same structured environment as airline crews, general aviation pilots probably won't have specific criteria unless employers prescribe them or the pilots take the time to calculate them before or during a flight. Sometimes, if you can just remember to have a Vref speed of 1.3 times stall in landing configuration as you go over the runway numbers, everything will be fine.

The FAA doesn't impose speed, descent or other numbers for landing various aircraft. You have to rely on your own research, what you've been taught, and the real-time judgment and performance facts you've accumulated through experience.

Most GA pilots have an advantage over pilots of jet airliners in that their piston engines and smaller aircraft are more immediately responsive. In fact, many may pride themselves on occasionally being able to turn an approach that's "all over the place" into a touchdown that has the tires barely kissing the pavement and the passengers being thoroughly impressed.

When salvaging an unstabilized approach doesn't quite work out, or the pilot hasn't recognized that a real problem exists, the NTSB will be called upon to explain what went wrong.

Beech C23
A Beech C23 on an instructional flight in day/VFR conditions was damaged during a hard landing on runway 09 at Campbell Airport (C81), near Grayslake, Ill. The instructor and student pilot were uninjured. The flight originated from Chicago Executive Airport (PWK).

The flight instructor stated that they had made two landings at C81, a stop-and-go and a full-stop and taxi back. The third landing was supposed to be a stop-and-go. The student reported it started getting dark, and he didn't see runway lights on. The airplane was configured with full flaps during final approach.

The student pilot said he knew that he maintained proper speed and altitude because the flight instructor didn't "complain" about it. The student pulled the throttle back to idle. He said he didn't know how far the airplane was above the runway when he pulled "too far back on the yoke," which made the airplane "slow too much and drop." The flight instructor exclaimed, "Power, power!" just before the airplane hit hard, bounced and banked to the right. The airplane slowed down and impacted the runway. The flight instructor then applied full engine power and performed an aborted landing. They then flew back to PWK.

The flight instructor told investigators that on the base leg of the third approach, the student was holding about 700 feet AGL and wasn't descending. The flight instructor told him to increase descent. The student reduced power and selected full flaps.

The instructor said the airplane was descending too fast, and he told the student to check the vertical speed indicator before they were on short final. The instructor said he took control of the yoke and put his hand over the student pilot's hand that was on the throttle to push the throttle forward. He said the student reacted by pulling the throttle backwards.

The NTSB said the probable cause of the accident was the inadequate flare by the student pilot and the inadequate supervision and delayed go-around performed by the flight instructor. Contributing to the accident was the student pilot's failure to attain and maintain a stabilized approach.

Piper PA-46-500TP
A turboprop Piper PA-46-500TP Meridian was destroyed when it impacted wires and terrain near Double Eagle II Airport (AEG), Albuquerque, N.M. The instrument-rated private pilot and his two passengers were fatally injured. Night/VFR conditions existed. The flight originated from Scottsdale, Ariz., and had been on an IFR flight plan that the pilot canceled.

Two witnesses who were in a Cessna 172 said that they heard the pilot announce his position on the Common Traffic Advisory Frequency as being eight miles southwest of the airport. He said that he was "entering an extended right downwind to runway 22, full stop at Double Eagle."

The Cessna 172 was departing upwind from a touch-and-go. The witness who was flying radioed that he would extend his upwind to give the pilot pattern spacing. The pilot responded with, "That won't be necessary, I'm a lot faster." The witness said that the Piper pilot told him to, "Go ahead and start your right crosswind."

The witness said that as he leveled off on downwind, it appeared that the airplane was at the same pattern altitude as the Piper, 6,800 feet. He said that he continued on the downwind and, at about midfield, he heard the Piper airplane call turning base, which was the last communication he heard from the pilot. He saw a "bright blue flash." After that it was completely dark, with no fire. Rescuers found that the airplane had struck power transmission wires about 8,200 feet from the runway threshold and broke a static wire.

Radar data from the FAA at Albuquerque International Airport indicated that the airplane entered the AEG traffic pattern from an extended downwind, at approximately 205 knots ground speed and an altitude of 6,800 feet MSL (1,000 feet AGL). Over the next approximately three nm on a downwind path, the airplane slowed to 171 knots ground speed and had descended to 6,300 feet MSL (500 feet AGL).

The radar data indicated that the airplane's downwind path moved about 2,000 feet closer to the runway and was approximately 2,775 feet away from the runway, when the pilot started his base turn. The last radar return showed the airplane at 5,900 feet MSL and 180 knots.

An engineer with the NTSB analyzed the last 28 seconds of the flight and estimated the maximum rate of descent while turning from base to final was between 1,800 and 1,900 feet per minute. The calibrated airspeed was estimated as between 145 and 150 knots. The NTSB engineer estimated that the maximum bank angle was approximately 73 degrees.

The Double Eagle II Airport is uncontrolled, and at an elevation of 5,837 feet. It has two runways: 22-04 which is 7,400 feet long, and 35-17 which is 5,999 feet long. Runway 22 has an ILS with a Medium Intensity Approach Lighting System with Runway Alignment Indicator (MALSR). Runway 22 isn't equipped with any visual glide path indicators. The airport's manager told investigators that local procedures recommend that airplanes fly a 1,000 feet AGL traffic pattern altitude and that large and turbine-powered airplanes should enter the traffic pattern at 1,500 feet AGL.

An instructor who taught at a facility where the pilot received training told investigators he teaches that downwind speed for the PA-46-500TP should be 145 to 150 knots, base 130 knots and final 90 to 95 knots, with maximum bank angles in the pattern of 30 degrees.

The NTSB determined that the probable cause of this accident was the pilot's unstabilized approach and his failure to maintain obstacle clearance. Contributing factors were the dark night and the static wires.

Peter Katz is editor and publisher of NTSB Reporter, an independent monthly update on aircraft accident investigations and other news concerning the National Transportation Safety Board. To subscribe, write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, N.Y. 10602-0831.