[NTSB Report, page 10]
The First Officer
[NTSB Report, page 11]
- According to American Airlines records, the first officer had flown Shorts 360, Beechcraft 99, and DeHavilland DHC-6 airplanes in commuter and regional operations under 14 CFR Parts 121 and 135. He had accumulated 3,220 hours total flying time in commercial and general aviation before his employment with American Airlines.
The first officer's background with large aircraft was very limited.
- American Airlines records also indicated that the first officer had accumulated 4,403 hours total flying time,26 including 1,835 hours as an A300 second-in-command. He had flown approximately 135 and 52 hours in the 90 and 30 days before the accident.
- An American Airlines captain who flew several times with the first officer on the 727 (when they were a junior captain and junior first officer, respectively) told Safety Board investigators that, during one flight sometime in 1997, the first officer had been "very aggressive" on the rudder pedals after a wake turbulence encounter. Specifically, the captain indicated that, when the airplane was at an altitude of between 1,000 and 1,500 feet, the first officer "stroked the rudder pedals 1-2-3, about that fast." The captain thought that the airplane had lost an engine and was thus focused on the engine instruments. The captain stated that he then asked the first officer what he was doing and that the first officer replied that he was "leveling the wings due to wake turbulence." The captain, who had his feet on the rudder pedals, thought that the first officer had pushed the rudder to its full stops.
- The captain did not recall what type of airplane the 727 was following. He thought that the wake turbulence encounter required only aileron inputs to level the wings but did not think that the first officer had made any such inputs during the encounter. The captain recalled being startled by the first officer's rudder inputs and indicated that they did not level the wings but created left and right yawing moments and heavy side loads on the airplane. He further indicated that the first officer did not need to be so aggressive because the 727 was "a very stable airplane."
- According to the captain, he and the first officer discussed this event later in the flight. The captain pointed out to the first officer that his use of the rudder pedals was "quite aggressive," but the first officer insisted that the American Airlines Advanced Aircraft Maneuvering Program (AAMP) directed him to use the rudder pedals in that manner. The captain disagreed with the first officer and told him that the AAMP directed that the rudder was to be used at lower airspeeds. The captain told the first officer to review the AAMP when he returned home and to be less aggressive on the rudder pedals when they flew together. The captain indicated that, during a wake turbulence encounter on a subsequent flight, the first officer modified his wake turbulence maneuver; specifically, the first officer used the rudder during the encounter but did not push the rudder to its full stop. The captain added that the first officer was still "very quick" on the rudder.
- The captain stated that he did not document or report this event at the time that it occurred. The captain further stated that he remembered the event with such clarity because he had never seen any pilot other than the first officer perform this maneuver.
There are statements from other crew members that both agree and disagree with this captain's assessment.
The Rudder Control System
Figure: Rudder Control System, from NTSB Report, Figure 6.
[NTSB Report, page 18]
- The rudder control system includes (1) the rudder pedals, the rudder trim actuator, the yaw damper actuator, and the yaw autopilot actuator, which command the rudder to move; (2) pushrods, bellcranks, a tension regulator, and cables (also referred to as linkages), which transmit rudder commands; (3) three servo controls (upper, middle, and lower), which operate the rudder; (4) a rudder travel limiter system, which provides a variable stop that limits rudder pedal travel with increasing airspeeds; and (5) a differential unit, which is a mechanical device that sends the rudder servo controls a command that is the sum of a pilot or an autopilot input and a yaw damper input. The maximum rudder deflection is 30o either left or right, the maximum rate of rudder movement (with no loads) is 60° ±5° per second, and the maximum rudder pedal displacement is 4 inches.
- At the public hearing for this accident, the vice president of Airbus' flight control and hydraulic department stated that the rudder was not normally used during cruise flight to control roll. The vice president of training for Airbus North America customer services stated that the ailerons and spoilers were used to control roll. This Airbus vice president also stated that the rudder was used to control yaw and sideslip and that the rudder "is not a primary flight control to induce roll under any circumstances unless normal roll control is not functional." He further stated that, if pilots were to experience a roll for any reason, "they will intuitively try and counter the roll with their normal roll control. If they exhaust their normal roll control, they will then go to rudder to try and induce a roll." He added that it would be "a long path to get down to that level of degradation to where a pilot would be exposed to using rudder."
This agrees with most of my experiences in jet aircraft, except those that are aerobatic in nature. I can see that a pilot brought up in light aircraft may not have the same "intuitive" understanding.
- Regarding the rudder travel limiter system, American Airlines' A300 fleet standards manager stated that, before the flight 587 accident, he thought that pilots knew "quite a bit" about the rudder limiter system but that, after the accident, it became apparent that pilots, as well as the aviation industry as a whole, "didn't know much about rudder limiter systems and in fact possibly had wrong perceptions." The A300 fleet standards manager also stated the following:
- Most pilots think that a limiter on some system will protect...the pilot from exceeding whatever parameter that limiter is limiting. And in this case...and it's not unique to Airbus aircraft...the pilots think that the rudder limiter will protect the aircraft structurally, and if it can't...they think...that there would be a limitation or a warning or caution or a note that would indicate...that the rudder limiter couldn't protect [the aircraft] structurally.
- Regarding the rudder pedals, the A300 fleet standards manager stated that, before the flight 587 accident, American Airlines did not teach its pilots during training that rudder pedal movement would become restricted as airspeed increased. The fleet standards manager also stated that he did not know that the rudder pedal movement would become restricted because the pedals are not normally pushed to the stop in flight. In addition, the fleet standards manager stated that, before the flight 587 accident, he did not think that any pilot would have thought that full rudder could be gained from about 1 1/4 inch of pedal movement and 10 pounds of pressure (above the breakout force) at an airspeed of 250 knots.
This is an unusual system and runs contrary to most rudder limiter systems. In the G450, for example, available rudder travel is indeed reduced at higher speeds.
[NTSB Report, page 18]
- The Safety Board developed a desktop computer simulation of flight 587 using A300-600 simulator model data provided by Airbus.
- The simulation indicated that, although external winds and moments, which were assumed to be attributable to the wake encounter, were required to match the airplane motion recorded on the FDR, the large roll and yaw oscillations, lateral load factors, and sideslip angles achieved during the accident sequence were the result of control wheel and rudder pedal inputs. The external winds and moments, by themselves, produced only an initial 10° deviation in bank angle (from the existing 23° bank angle) and only subtle changes in heading, resulting in sideslip angles of less than 2.5°.
American Airlines Advanced Maneuvering Program (AAMP)
[NTSB Report, page 18]
- AAMP development began in 1996 after a review of worldwide accidents from 1987 to 1996 involving large multiengine transport-category airplanes128 found that the leading causal factor for these accidents was loss of control. According to American Airlines, the aviation industry believed that many of the accidents might have been prevented if the pilots had been trained to specifically recognize and respond to airplane upsets.
- The booklet that the accident pilots received during their initial AAMP training was dated January 1, 1997. That booklet contained the following information regarding pilot responses to wake turbulence:
- Rolling moment on aircraft with shorter wing spans can be dramatic.
- Resulting attitude may be nose low with more than 90° of bank.
- Apply the appropriate unusual attitude recovery procedure.
- Do not apply any back pressure on yoke at more than 90° of bank. ROLL FIRST – THEN PULL.
- High AOA maneuvering = RUDDER.
- Corner speed – high lift devices extended.
These are very good points for a low speed aircraft upset recovery. They would work for a higher speed, but the aircraft would have to be unloaded (flown at zero g) first.
- [A] videotape on unusual attitude recoveries was dated December 19, 1997, and was made during an actual AAMP training class that occurred during either March or April 1997. The class was attended by about 200 company pilots and was taught by the AAMP course developer. The unusual attitude recoveries videotape emphasized the smooth application of rudder with small inputs for coordinated use and suggested avoiding, at high AOAs, large rudder inputs that would induce large sideslip angles. The videotape discussed information about lead and lag response times for the rudder and emphasized that a lack of understanding of the rudder could lead to overcontrolling the airplane. The videotape also demonstrated a high AOA control application in the simulator. The instructor on the videotape stated the following regarding recovery from unusually nose-high situations:
- Now some of you [pilots attending the AAMP training class] out there might say 'well, I'm going to use a little coordinated rudder to help the nose come down.' Fine, that's fine, that's good technique. A little, OK, smoothly applied, I mean, understand right here: if you jam full right rudder, that's the spin entry procedure, see?
Here again, excellent points. But I wonder how many of the audience understood the implications had they not been spin trained?
- In a May 22, 1997, letter to the chief test pilot at Airbus, an American Airlines A300 technical pilot indicated his concern that AAMP handout pages stated that "at higher angles of attack, the rudder becomes the primary roll control." The technical pilot's letter also expressed concern that "the program infers that aileron application in these situations is undesirable since it will create drag caused by spoiler deflection." Further, the letter stated that the AAMP instructor had been teaching pilots to use the rudder to control roll in the event of a wake turbulence encounter. The American Airlines A300 technical pilot asked the Airbus chief test pilot for his thoughts on this subject and suggested a teleconference a few days later. In a May 23, 1997, facsimile, the chief test pilot stated that he shared the A300 technical pilot's concern about the use of rudder at high AOAs and agreed to a teleconference to discuss the matter.
- In a June 13, 1997, internal letter to colleagues, the Airbus chief test pilot indicated that he had spoken with American Airlines. The letter detailed the chief test pilot's general views regarding the use of the rudder at low airspeeds and the use of flight training simulators, which he had discussed during the teleconference. The letter stated that, although the rudder becomes more effective for roll control as airspeed is reduced, normal lateral control (aileron and spoilers) is effective down to the stall speed. The letter indicated Airbus' recommendation to use the rudder as necessary to avoid sideslip but not as the primary source of roll. The letter also indicated that flight training simulators could not be expected to be accurate at the edges of the flight envelope and did not include dynamic maneuvers outside the normal flight envelope. In addition, the letter stated that simulators were "particularly inaccurate for large sideslip angles" and that a pilot might draw the wrong conclusion from maneuvers involving the use of rudder at low airspeeds.
- Regarding the use of rudder, [a Boeing] letter stated that "the excessive emphasis on the superior effectiveness of the rudder for roll control vis-à-vis aileron and spoilers, in high angle of attack, is a concern" and that a more appropriate standard would be to first use the full aileron control and, if the airplane is not responding, to then use rudder as necessary to obtain the desired airplane response.
- In a letter dated October 6, 1997, American Airlines' chief pilot and vice president of flight responded to the letter from the representatives from the Boeing Commercial Airplane Group, the Boeing Douglas Products Division, Airbus, and the FAA. The chief pilot and vice president of flight explained that American Airlines does not advocate using "rudder first" or "rudder only." Also, he pointed out that four different sections of the AAMP emphasized that, when an airplane is not responding to aileron and spoiler control, smooth application of coordinated rudder should be used to obtain the desired roll response.
The accident first officer apparently did not understand this and it appears many of his peers were in the same boat.
A pilot's over-aggressive use of the rudder may have been abetted by the knowledge they were below design maneuvering speed. The flight of American Airlines 587 provides a good case study:
[NTSB Report, ¶2.5.3]
- During this accident investigation, the Safety Board learned that many pilots might have an incorrect understanding of the meaning of the design maneuvering speed (VA) and the extent of structural protection that exists when the airplane is operated below this speed.
- From an engineering and design perspective, maneuvering speed is the maximum speed at which, from an initial 1 G flight condition, the airplane will be capable of sustaining an abrupt, full control input limited only by the stops or by maximum pilot effort. In designing airplanes to withstand these flight conditions, engineers consider each axis (pitch, roll, and yaw) individually and assume that, after a single full control input is made, the airplane is returned to stabilized flight conditions. Full inputs in more than one axis at the same time and multiple inputs in one axis are not considered in designing for these flight conditions.
- The American Airlines managing director of flight operations technical told the Safety Board, during a post accident interview, that most American Airlines pilots believed that the airplane would be protected from structural damage if alternating full rudder pedal inputs were made at an airspeed below maneuvering speed. The American Airlines A300 fleet standards manager confirmed this belief during testimony at the Board's public hearing for this accident. The Board notes that the American Airlines A300 Operating Manual contained only one reference to design maneuvering speed, which indicated that it was the turbulence penetration speed (270 knots). However, as evidenced by flight 587, cyclic rudder pedal inputs, even when made at airspeeds below maneuvering speed, can result in catastrophic structural damage.
- Existing regulations and guidance pertaining to maneuvering speed may have contributed to the misunderstanding regarding the degree of structural protection provided by operating below maneuvering speed. Title 14 CFR 25.1583, "Operating Limitations," lists maneuvering speed among the airspeed limitations that must be furnished to the pilots of transport-category airplanes and states that, along with maneuvering speed, pilots must also be furnished "with a statement that full application of rudder and aileron controls, as well as maneuvers that involve angles of attack near the stall, should be confined to speeds below this value." Although it is true that full control inputs should be confined to airspeeds below maneuvering speed, the statement in Section 25.1583 could also be read to incorrectly imply that an airplane could withstand any such inputs so long as they were made below maneuvering speed. The explanation of design maneuvering speed in AC61-23C, "Pilot's Handbook of Aeronautical Knowledge," may be even more misleading, stating that, "any combination of flight control usage, including full deflection of the controls, or gust loads created by turbulence should not create an excessive air load if the airplane is operated below maneuvering speed." This statement strongly—and incorrectly—suggests that, if multiple control inputs were made below maneuvering speed, the airplane would be protected against structural damage.
- The Safety Board has no reason to believe that the misunderstanding about maneuvering speed is limited to A300-600 pilots. As a result, the Safety Board concludes that there is a widespread misunderstanding among pilots about the degree of structural protection that exists when full or abrupt flight control inputs are made at airspeeds below the maneuvering speed. Therefore, the Safety Board believes that the FAA should amend all relevant regulatory and advisory materials to clarify that operating at or below maneuvering speed does not provide structural protection against multiple full control inputs in one axis or full control inputs in more than one axis at the same time.
Design Maneuvering Speed, VA, is an aircraft certification number of the manufacturer's choosing. It changes with weight, configuration, and altitude. Unless you have a complete chart in front of you, it may be meaningless in most specific instances. You should never manipulate a flight control faster than you can perceive the changes that result.
More about this: VA - Maneuvering Speed.