Aviation

Aeronautical Common Sense

Three weeks ago, I read to William Langewiesche’s Vanity Fair piece on Air France 447, a crash into the Atlantic Ocean that took the lives of 228 on 1 June 2009; those 228 deaths crying out for a total revamp of air carrier stall recovery procedures:

It seems that we are locked into a spiral in which poor human performance begets automation, which worsens human performance, which begets increasing automation. The pattern is common to our time but is acute in aviation. Air France 447 was a case in point. In the aftermath of the accident, the pitot tubes were replaced on several Airbus models; Air France commissioned an independent safety review that highlighted the arrogance of some of the company’s pilots and suggested reforms; a number of experts called for angle-of-attack indicators in airliners, while others urged a new emphasis on high-altitude-stall training, upset recoveries, unusual attitudes, flying in Alternate Law, and basic aeronautical common sense. All of this was fine, but none of it will make much difference. At a time when accidents are extremely rare, each one becomes a one-off event, unlikely to be repeated in detail.

(Emphasis mine).

Sorry, Mr. Langewiesche, you are completely wrong. AF 447 rewrote the book on stalls.

The August 2012 Revamp

Five years ago, U.S. aviation authorities essentially threw the dead bodies of Marvin Renslow and Rebecca Shaw under the bus. The two pilots of CO 3407, a Colgan Q400 that stalled and crashed on 12 February 2009 on approach to Buffalo International Airport were smeared mercilessly, blamed for not adhering to Colgan’s highly inappropriate stall recovery procedures:

What Procedures Caused This Crash?

This is the question the author feels that all accident investigators should ask first and foremost.  Naturally, questioning the procedures of powerful businesses and governmental organizations is not a common occurrence in this country.  Nevertheless, the NTSB really should have recognized that this is not at all appropriate:

Stall profile Entry into stall During stall Exit from stall
Landing stall 180 knots and minimumaltitude of 5,000 feet AGL [(Above Ground Level)] with flaps at 35°, gear down, and power at flight idle  PF maintains altitude andHeading PF calls “stall,” advancespower to rating detent, andcalls “check power, flaps 15” PM calls “positive rate” PF calls “gear up.” 

PM calls “Vfri”

 

PF calls “flaps 0”

 

PF adjusts power tomaintain 180 knots 

Maintain altitude.  Essentially, air carrier training emphasized “powering out” of a stall—maintaining (or possibly increasing) pitch attitude so as to avoid any altitude loss or gain.  This was industry-standard in 2009, and today is rightly considered borderline psychotic:

(D) Reducing AOA is the proper way to recover from a stall event. Pilots must accept that reducing the aeroplane’s AOA may often result in altitude loss. The amount of altitude loss will be affected by the aeroplane’s operational environment (e.g., entry altitude, aeroplane weight, density altitude, bank angle, aeroplane configuration, etc.). At high altitudes, stall recovery may require thousands of feet,

(E) Differences between high and low altitude stalls; pitch rate and sensitivity of flight controls, thrust available for recovery, and altitude loss,

(F) The need to apply nose down elevator inputs to reduce AOA when stalled at excessively low pitch attitudes and/or at large bank angles, including bank angles exceeding ninety degrees,

(G) Noises associated with stick shakers and autopilot disconnect aural alerts or alarms can cause confusion in the cockpit,

(H) Understanding that early recognition and return of the aeroplane to a controlled and safe state are the most important factors in recovering from stall events. Only after recovering to a safe manoeuvring speed and AOA should the pilot focus on establishing an assigned heading, altitude, and airspeed

That’s right—Transport Canada essentially threw stall recovery heading and altitude control requirements out the window (an eminently sensible approach, given that heading and altitude aren’t much help if the plane slams into a house on final to Runway 23 at BUF).  Current Q400 stall recovery procedures seem to have been copied-and pasted from the Canadian regulatory agency:

Stall Warning Recovery
The flight crew shall use all energy resources available, including altitude, as appropriate, to prevent or recover from a stall condition. HGS guidance should be used, if available.  
Stall Recovery Summary
At first sign of stall:
1. Increase airspeed by:
• Reducing pitch (altitude permitting)
• Adding power
2. Roll wings level.
3. Increase airspeed out of stall condition ≥ Low-speed Cue + 10 knots.
4. Recover to Missed Approach or appropriate flight regime. CAUTION:
Be prepared to manage control forces for required pitch inputs.
• An actual stall results in a nose-down pitch, especially if the stick pusher activates (70 lbs). Too much forward movement of the control column can produce an excessive nose-down attitude.
• As power and airspeed are increased, a pitch-up tendency may be induced.
• G/A is pressed to set a maximum pitch limit during recovery.
Reduce pitch below the Flight Director as necessary during recovery.

Before this begins to sound too pro-Great White North, I would be remiss to ignore AC-120-109:

Emphasis Items.

The following items should be emphasized during maneuver-based training:

(a) How changes to factors such as weight, G loading, bank angle, altitude and icing affect the handling characteristics and stall speeds of the airplane.

(b) Abrupt pitch up and trim change commonly associated when the autopilot unexpectedly disconnects during a stall event. This dramatic pitch and trim change typically represents an unexpected physical challenge to the pilot when trying to reduce AOA. In some airplanes, this may be exacerbated by an additional pitch up when the pilot increases thrust during stall recovery.

(c) Stall warnings for the specific airplane.

(d) Reducing AOA is the proper way to recover from a stall event. Pilots must accept that reducing the airplane’s AOA may often result in altitude loss. The amount of altitude loss will be affected by the airplane’s operational environment (e.g., entry altitude, airplane weight, density altitude, bank angle, airplane configuration, etc.).  At high altitudes, stall recovery may require thousands of feet.

(e) Noises associated with stick shakers and autopilot disconnect alarms can cause confusion in the cockpit.

(f) Understanding that early recognition and return of the airplane to a controlled and safe state are the most important factors in surviving stall events (only after recovering to a safe maneuvering speed and AOA should the pilot focus on establishing an assigned heading, altitude, and airspeed).

(g) Differences between high and low altitude stalls; pitch rate and sensitivity of flight controls, thrust available for recovery, and altitude loss.

This FAA Advisory Circular predates the Transport Canada document by a year.  Yet AC 120-109 is from August 2012—three and a half years after the Colgan crash.  I’m going to go out on a limb, and postulate the complete revamping of air carrier stall recovery procedures (more of a back to basics—after all, “lower the nose” is not news to pilots) wasn’t related to the investigation of CO 3407.

Turns out the BEA’s crash report on AF 447 was released in July 2012—the month prior to AC-120-109. See if an astute reader can spot the problem in Air France’s stall recovery procedures:

1.18.3.5 Airline training

1.18.3.5.1 Crew training

Stall phenomena are covered during the initial A320 type rating, according to the same philosophy of the manufacturer and the operator. They are not reviewed during the long haul passage, in CCQ 330, or during recurrent training.

At the time of the accident, the immediate actions were: simultaneously reducing angle of attack and applying TOGA thrust from the first signs of the stall (Stall warning / buffet onset). A minimal loss of altitude was expected.

Minimum loss of altitude—this was the catch-all standard that prevailed worldwide before AC-120-109. But it was a dangerous and foolhardy standard:

Though precise modeling was never pursued, the investigators later estimated that this was the last moment, as the airplane dropped through 13,000 feet, when a recovery would theoretically have been possible. The maneuver would have required a perfect pilot to lower the nose at least 30 degrees below the horizon and dive into the descent, accepting a huge altitude loss in order to accelerate to a flying angle of attack, and then rounding out of the dive just above the waves, pulling up with sufficient vigor to keep from exceeding the airplane’s speed limit, yet not so violently as to cause a structural failure.

Stall recovery might require 13,000 feet or more altitude to recover, which needless to say is incompatible with “minimize altitude loss.” FAA practical test standards (checkrides for certificate or rating issue) require pilots to perform aerial maneuvers while maintaining an assigned altitude +/- 100 feet, and pilots can be violated operationally for deviating more than 300 feet from an ATC-assigned altitude. Prior to August 2012, a systemic procedural and regulatory bias prevented training to the physical realities of stalled aircraft.

Apologies to the FAA (But You Still Should Have Known Better)

I have been less than charitable with my accusations that the U.S. federal government ducked responsibility for the enduring disaster. The chain of poor regulatory policy seemed damning in the NTSB report on CO 3407:

The NTSB did not argue that stall recovery procedures should be completely rewritten as a result of the February 2009 crash, though the NTSB was clearly aware of the problem:

Also, on July 29, 1997, the NTSB issued Safety Recommendation A-97-47 as a result of the ABX Air accident in Narrows, Virginia.  Safety Recommendation A-97-47 asked the FAA to do the following:

Evaluate the data available on the stall characteristics of airplanes used in air carrier service and, if appropriate, require the manufacturers and operators of flight simulators used in air carrier pilot training to improve the fidelity of these simulators in reproducing the stall characteristics of the airplanes they represent to the maximum extent that is practical; then add training in recovery from stalls with pitch attitudes at or below the horizon to the special events training programs of air carriers.

Not exactly “lower the nose,” but the NTSB in 1997 came extremely close with “pitch attitudes at or below the horizon.”  The FAA in response generated the inadequate stall recovery standard in effect from 1999 to 2012:

The FAA further stated that, to address the recommendation, it would revise the practical test standards to require pilots to adjust pitch, bank, and power to recover from an approach to stall and would add a note indicating, in part, that airspeed and/or altitude loss is critical at low altitudes and must be kept to an absolute minimum.

Eight months ago I concluded the “minimum loss of altitude” standard migrated to airline procedures from the FAA’s inappropriate response to A-97-47, which unfortunately for the pilots of an ABX DC-8 was not the case:

1.18.3 Survey of Stall Recovery Procedures

The Safety Board examined stall recovery procedures outlined in ABX’s DC-8 operations manual and those recommended by the airplane’s manufacturer. According to the introductory section (page 4) of ABX’s DC-8 operations manual, dated December 31, 1988, stall recovery is to be accomplished “sufficiently smooth to avoid sustained secondary indication of approach to stall while minimizing altitude loss.”

Minimizing altitude loss—the same flawed stall recovery standard was present in airline procedures dating from 1988. If it is not already clear, this is an excerpt from the NTSB report on the crash of an ABX Air DC-8 in Narrows, Virginia on 22 December 1996; the same report which generated A-97-47:

The ABX DC-8 operations manual prescribes stall recovery practice procedures to be accomplished between 10,000 feet and 15,000 feet agl. For zero flap clean stalls, the manual describes the sequence of operations as follows: an initial entry speed of 200 knots, straight and level, slow deceleration by reduction of power to “minimum ‘spool up’ rpm, maintaining heading and altitude. Maintain altitude by increasing pitch, maintaining the rate of climb indicator at zero rate of climb.” It said to discontinue trimming below 1.5 Vs. The manual described the recovery as follows:

At ‘stick shaker’ or initial buffet, apply and call out ‘Set Max Power.’ Simultaneously reduce back pressure sufficiently to stop the stick shaker. Fly the airplane out of the buffet. There should be very little, if any, altitude loss. The PF should observe the trim changes as the engines accelerate.

The 1988 ABX manual (section 00, pages 54-55) further stated:

The primary purpose of stall practice is to enable the pilot to avert a dangerous stall condition by early stall recognition, followed by immediate corrective action. It should be remembered that a stall recovery is accomplished by reducing the angle of attack at which the airplane is flying. This may be accomplished by a number of ways, but basically by (1) lowering the pitch attitude, (2) acceleration produced by adding thrust and/or (3) by leveling the wings, if in a bank.

All stall approaches should be made only to the ‘stick shaker’ or initial buffet, whichever occurs first. Points to be stressed are a smooth entry, striving for a zero rate of climb, and a prompt, well coordinated recovery without inducing a secondary stall. The altitude lost in stall recovery depends on the promptness and smoothness of applying the recovery technique, i.e., lowering the pitch attitude, applying power and leveling the airplane.

The manual added, “Particular care should be exercised to ensure that the buffet has ceased before the airplane is rotated nose up for recovery. Additionally, the controls should be moved smoothly to preclude inducing acceleration loads which could cause secondary stall indications.”

According to a draft of a new ABX operating manual, dated October 15, 1996, and written by the accident PF, the DC-8 was “designed to have good stall characteristics. Longitudinal stability is positive below the stall, and there is a strong pitch down tendency after the stall. Light buffet may be felt prior to the stall, although artificial stall warning from the stick shaker will occur about 10 percent above the 1 G stall speed.” The manual, which had not been approved at the time of the accident, stated that the initial buffet on the DC-8 “occurs very close to actual stall speeds.”

The draft of the new ABX operating manual was written by the pilot flying (PF) the accident aircraft? Yes. The three men composing the flight crew of the DC-8 were all senior flight standards managers:

The PNF, age 48, was hired by ABX in March 1988 as a DC-8 first officer. He later was promoted to DC-8 simulator instructor and, in 1990, to DC-9 flight standards pilot. After a brief period as a DC-9 line captain, he was promoted in 1994 to DC-8 flight standards manager and to B-767 flight manager in July 1996, in anticipation of the planned delivery of Boeing B-767 airplanes to the ABX fleet. He was also an FAA-designated DC-8 examiner.

[The PF] was hired by ABX in April 1991 as a DC-8 first officer and completed his initial operating experience (IOE) that June. In August 1993, he was promoted to DC-8 equipment chief pilot and was assigned as a DC-8 standards pilot in May 1996. He was promoted to manager of DC-8 flight standards in June 1996, replacing the accident PNF in that position. He had also been selected to become an FAA-designated DC-8 examiner.

The flight engineer, age 52, was hired by ABX as a DC-8 flight engineer in February 1988 and was promoted to DC-8 flight standards flight engineer in May 1991.

There were three Jacob Veldhuyzen van Zantens in the cockpit of this DC-8. Like the senior Dutch pilot and his two fellow crewmembers nearly twenty years prior, the three senior ABX crewmembers made basic mistakes that killed everyone aboard their four-engine jet:

3.2 Probable Cause

The National Transportation Safety Board determines that the probable causes of this accident were the inappropriate control inputs applied by the flying pilot during a stall recovery attempt, the failure of the nonflying pilot-in-command to recognize, address, and correct these inappropriate control inputs, and the failure of ABX to establish a formal functional evaluation flight program that included adequate program guidelines, requirements and pilot training for performance of these flights. Contributing to the causes of the accident were the inoperative stick shaker stall warning system and the ABX DC-8 flight training simulator’s inadequate fidelity in reproducing the airplane’s stall characteristics.

Or did they?

The flightcrew had initiated the clean stall maneuver at 13,500 feet, within a block altitude range of 13,000 feet to 15,000 feet. Their use of the lowest 500 feet of the block altitude indicated that the flightcrew anticipated recovering from the stall with a minimum altitude loss, just as they were accustomed to performing and instructing the standard ABX stall maneuvers in the simulator. Further, their execution of the clean stall only slightly above the cloud tops suggests that the flightcrew did not anticipate the possibility of greater altitude loss.

The DC-8 flight crew, all three being flight managers for the aircraft type, treated a stall as a non-event…and were killed for their trouble. There really is no other way to say this—air carriers ignored a basic threat to air navigation for decades. Common sense is not as common as it appears at first.

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One thought on “Aeronautical Common Sense

  1. Pingback: Navigating Aeronautical Safety–Part 3 | In The Corner, Mumbling and Drooling

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