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© APS |
While most would agree that aviation is an inherently risky endeavour, technological advancements and improved aircrew training have continued to reduce the accident rate for commercial air operations.
According to Boeing's 2007 Statistical Summary of Commercial Jet Airplane Accident: Worldwide Operations: 1959-2006, the two leading causes of fatalities have been controlled flight into terrain (CFIT) and in-flight loss of control (LOC), with each accounting for about the same number of fatalities. By 2009, however, Boeing had noted a two-to-one reduction in the number of CFIT events compared with LOC.
The decrease in CFIT fatalities can be attributed to the development and deployment of terrain awareness and warning systems, ground proximity warning systems and Honeywell's EGPWS. Despite a concerted industry-wide effort, there has been no corresponding dramatic reduction in LOC fatalities. Complicating matters is that reduced separation minimums that will be made possible by the USA's next-generation satellite-based air transport system could increase the number of wake vortex encounter generated LOC incidents.
TECHNOLOGY
Two major avenues are available for the reduction of LOC accidents - better aircraft and improved aircrew training. The latter is the focus of a joint venture by Aviation Performance Solutions, a Mesa, Arizona-based provider of upset recovery training, and simulation powerhouse CAE, which are introducing a programme for their business and airline clients.
Arguably the most visible progress has been made down the better-aircraft avenue. The stall-spin accident, once the bane of aviators, has nearly been eliminated by aircraft certification requirements. Fly-by-wire control systems offer even greater prospects of reducing LOC accidents.
Airbus and Boeing FBW control systems offer some level of envelope protection. Airbus logic will not allow bank angle to exceed 67°. Boeing's requires the pilot to use additional roll force to exceed 35° of bank, but with no ultimate limit in bank angle. In the pitch axis, both systems work to prevent high and slow speed excursions. Airframe load limits are actively protected in the Airbus, while Boeing gives the pilot the final say on just how much g force is really needed.
While the several manufacturers have differing views on envelope protection schemes, FBW control systems can be mechanised to prevent a sizable percentage of LOC accidents.
Autopilot mechanisation is another area where technology is being used to prevent LOC accidents. The autopilot in the Garmin G1000-equipped Cirrus SR22 has a "LVL" button. If disoriented the pilot can push the panic button, with the autopilot levelling the wings and bringing the pitch attitude to level flight.
Perhaps the ultimate panic button for a disoriented pilot is the ballistic parachute available in some general aviation and light sport aircraft. Deployment will result in a hull loss, but at least the occupants will live.
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© APSAPS uses an Extra 300L to teach pilots hot to react to upsets |
On the training side of the equation, I have witnessed an erosion in the basic flying skills as aircraft have become "safer". Modern aircraft are not supposed to spin, so spin recovery is not taught to the large majority of pilots. While the multi-crew pilots licence (MPL) calls for exposure to aerobatics in a light aircraft, it is conceivable that the captain of your transatlantic flight has never been upside down in a real aircraft. In training simulations large transport aircraft are not stalled, rather an approach to stall manoeuvre is taught.
The approach to stall is in reality an instrument proficiency manoeuvre, where the pilot is judged on how well he or she maintains altitude as the aircraft powers out of the slow speed condition. Documented incidents of high-altitude stalls in transport aircraft, some fatal, highlight the deficiency of this practice.
In the typical high-altitude stall incident, the pilots have tried to maintain altitude while applying maximum thrust. Once on the back side of the power curve, however, the only way to recover the aircraft is to trade altitude for airspeed. Executing an approach to stall recovery in a high-altitude stall condition will not in all likelihood recover the aircraft.
The industry reference for the prevention of LOC accidents in swept-wing jet transport aircraft is the Boeing/Airbus Airplane Upset Recovery Training Aid, Rev 2 manual, available online from a number of sources including the US Federal Aviation Administration.
A smaller and more user friendly guide to aircraft upset recovery training is the Royal Aeronautical Society's Introduction to aeroplane upset recovery training: History, core concepts and mitigation.
Upset recovery training is conducted by most airlines, typically as part of recurrent training profiles, in the classroom and simulator. Airbus has recommended that upset recovery training should not be conducted in a flight simulation training device because simulator motion does not accurately represent aircraft motions in unusual attitudes and there is a lack of validated flight envelope model data at extreme conditions.
In addition, most simulator upset recovery training is conducted with the motion on, which may not increase the value of the training. Current devices can only simulate 1g flight, a fleeting condition in the early stages of an upset recovery.
Simulation may even provide strong negative training, as was the case in the crash of American Airlines flight 587 in New York in 2001. Inappropriate aggressive rudder usage to counter wake turbulence-generated rolling motions caused the Airbus A300's vertical stabiliser to snap off. At the time American Airlines had been teaching the use of rudder to help in upset recovery. While the A300 simulator may have accurately represented aircraft response to rudder inputs, it was not an engineering loads simulator and the crews would not have be alerted to the excessive structural loads their inputs were generating.
TRAINING CHOICES
Continued LOC events are forcing aircraft operators and regulators to re-evaluate how upset recovery prevention and recovery training is conducted. There are three channels available to deliver such training: academic (classroom or online); ground-based simulator; and aircraft.
The aircraft channel might further be divided into actual aircraft, surrogate and generic. Use of any aircraft to teach upset recovery carries with it risk that must be balanced by the usefulness of the received training. Use of the actual aircraft for training may be limited by the size of their flight envelope and their operational expenses.
For fighter types, in-aircraft training may be the way to go, but for transport category aircraft it is out of the question. The surrogate option is perhaps best typified by Calspan's variable stability Bombardier Learjet, an aircraft that can be programmed to fly like a large transport aircraft or business jet while also allowing for in-aircraft demonstration of various control system failures.
Generic-class aircraft, the tools that make up part of the CAE/APS programme, range from single-engined piston Beech Bonanzas and Extra 300Ls to the Aero Vodochody L-39 jet, aerobatic aircraft that offer a large flight envelope and are relatively inexpensive to operate. A generic aircraft will not fly like the actual aircraft, and unique/specific actual aircraft procedures should not be taught in them.
EMERGENCIES
APS has developed and taught for several years a comprehensive upset recovery course. Its venture with CAE offers upset recovery training for business and airline clients. In the past CAE had offered APS's web-based course, based on the 443-page Boeing/Airbus manual. Now APS's simulator and in-flight training modules will also be offered as part of the four-day "graduated" training programme.
In addition to using Extra 300L propeller aircraft and an Embraer ERJ-145 full-flight simulator, APS is purchasing an L-39 jet trainer. This comprehensive three-pronged training approach to LOC prevention may well be pacing the industry.
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© APSOtter McNeace gives a briefing on inverted nose-low recoveries |
APS's online pilot training manual, written by staff members, provides a brief primer on basic flight theory, spatial disorientation and its causes, all-attitude upset recovery (AAUR) procedure, spin recovery procedure and a detailed list of in-flight exercises.
In-flight training is conducted in one of the company's fully aerobatic Extra 300L. My instructor was J "Otter" McNeace, director of flight training and standards for APS. Otter has military and civil flight experience, first as a US Navy Boeing F/A-18 Hornet "Top Gun" graduate, followed by a 10-year stint as a Boeing 737 pilot at a US airline.
After meeting APS's president, Paul Ransbury, Otter and I settled into a briefing room for a pre-flight briefing. Having instructed in high angle of attack flight at the USAF Test Pilot School, I found much of Otter's briefing to be a review of topics I was quite familiar with. Aside from his in-depth subject knowledge, I was impressed with his enthusiasm for the teaching upset recovery techniques.
After explaining that our 1h flight in the Extra would be used to show me a smattering of the exercises flown during their several multi-flight emergency manoeuvre training courses, he went over APS's five-step AAUR procedure: push, power, rudder, roll and climb.
- Push the yoke forward to unload the aircraft. As g load is reduced, stall speed decreases. At zero g the wing, no matter the attitude, cannot be stalled. For APS's purposes a 1/2g unload is the desired target.
- Power Retarded or advanced?
- Rudder Unless there is a failure it should be centred.
- Roll to level the wings.
- Climb Establish a climb to complete the recovery.
APS advocates a "say and do" method while executing the recovery. Not only does saying a step reinforce its application, it has benefits in a crew environment. In an upset situation both pilots may be disoriented. By announcing the recovery step, the pilot flying shows he is in charge and taking steps to recover the aircraft to controlled flight. Saying each recovery step establishes its validity and may stop a disoriented pilot from interfering in the recovery.
As spins would be part of the Extra 300L flight, Otter discussed the philosophy of an alternate control strategy. In the above AAUR procedure, the aircraft responds as expected to control inputs. An alternate control strategy is employed in situations where normal control inputs will not have the expected results.
In a developed spin, pushing the stick forward alone may not provide enough pitch authority to break the stall. Only after the yaw rate has been stopped or slowed will forward stick break the stall. For spin recoveries APS teaches the NASA standard spin recovery - PARE (power, ailerons, rudder, elevator).
- Power is retarded to idle.
- Ailerons are neutralised.
- Rudder Full rudder is applied opposite the spin direction.
- Elevator Full forward elevator is applied.
After rotation stops the rudder is neutralised and elevator applied to recover from the dive. United Airlines flight 232 is another example of an alternate control strategy. After losing all hydraulic power in a McDonnell Douglas DC-10, the crew of UA232 successfully used differential engine thrust to land the stricken aircraft at Sioux City, Iowa.
A fully developed spin represents the most predictable event necessitating an alternate control strategy, but any number of failures could require creative use of flight controls and power to recover to controlled flight.
STARTLE FACTOR
With the academics over, we proceeded to strap into one of APS's Extra aircraft. I was in the front seat with Otter in the aft. Otter started the aircraft and performed the take-off from Mesa's Williams-Gateway airport, the former USAF Williams AFB. Our manoeuvre area was just minutes away to the east of the field and the 300hp (225kW) Extra rapidly climbing to 8,000ft (2,440m).
En route I familiarised myself with the Extra, marvelling at its light control forces. The nearly full span ailerons generated rapid roll rates, with the rudder able to generate large angles of sideslip. In short, the Extra flew nothing like a swept wing transport category aircraft, but during my flight it would be put to good use demonstrating lessons applicable to all categories of pilot.
One of the first manoeuvres we did was a series of 60° angle of bank steep turns. As most civil aircraft lack a g meter, this helped calibrate our bodies to what a 2g pull-up would feel like. Next we did several 1g unaccelerated stalls, to practise and gain confidence in the AAUR procedure.
The Extra has a 1g stall at and indicated air speed of around 60kt (110km/h) and the stalls experienced were quite benign. Most pilots are familiar with accelerated stalls and realise that stall speed increases as g loading increases.
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© APS |
Academically most pilots know that as g load decreases, so does the stall speed. The stress of flight and unusual aircraft attitudes can make academic knowledge fleeting, however. The next exercise was a zoom manoeuvre to see in-flight how stall speed decreases with g load.
A pull to 70° nose high attitude was initiated at 120kt. As the aircraft slowed through 70kt I eased forward on the stick to feel light in the seat, with a target of 1/2g.
At the top of arc, indicated airspeed had decreased to less than 40kt, well under the 1g stall speed, yet the aircraft was flying with good control authority in all three axes.
Having built my confidence in the Extra 300L and the "say and do" method of implementing the AAUR procedure, we moved on to the heart of the in-flight exercise programme: unusual attitude recoveries.
Both nose-high and nose-low attitudes were presented, with recovery initiated upon Otter's command. The attitude indicator in the front cockpit had been blanked out, forcing me to reference the real world for the recoveries.
To simplify the nose-high recovery procedure Boeing is recommending that crews simply unload the aircraft and not use large bank angles to speed the drop of nose to the horizon. This method worked well, rapidly recovering the Extra to straight and level flight.
The nose-low unusual attitude was a real eye opener. When prompted to recover, the Extra was in a 30° dive and over-banked to 120°. Inverted and faced with a face full of brown desert, some startled pilot's gut reaction would be to immediately do the wrong thing and pull back on the stick.
Using APS's AAUR procedure led me immediately push on the stick to unload the Extra and rapidly roll it upright before initiating a pull to the horizon.
Even if the pilot would roll the wrong way to get to the horizon, the aircraft is in a much better position than if the pilot were to pull more gs. The strength of the "say and do" method is that it ingrains a positive response to an unusual attitude, overcoming any fear or hesitation generated by the extreme flight attitude.
Our final exercise was a fully developed upright spin demonstrated by Otter. After about six turns, he used the NASA standard recovery to recover the aircraft. Yaw rotation stopped in less than one turn after he had applied opposite rudder, with forward stick breaking the stall.
SIMULATED MANOEUVRES
The final third of the CAE/APS upset recovery training programme is a session in a CAE Level D ERJ-145 simulator. As mentioned, it is recognised that conventional simulators have numerous limitations that may limit there effectiveness for teaching upset recovery procedures. Valuable lessons can be taught and learned in a simulator, but all must realise that the sterile simulator environment will not replicate visceral experience of in-aircraft upset recovery event.
I have spent countless hours in transport category aircraft simulators and instantly felt at home in the ERJ-145. I took the left seat and Otter the right. After take-off we climbed to medium altitude for a series of control response exercises. Here we explored the effect of changing power settings and the extension of speed brakes on the pitch axis of the aircraft.
While pitch changes due to power are relatively small in the ERJ, for a 737 they are quite pronounced as the engines are mounted below the wing and cause a pitch up when power is advanced.
The most interesting exercise was to compare the effectiveness of using ailerons and spoilers to roll the aircraft and just using the rudder. This exercise showed that while rudder would roll the aircraft, precisely controlling bank angles was more difficult with the rudder than with the aileron/spoiler combination.
We also performed two stalls, one at medium altitude and one at high altitude. The medium altitude stall was in straight and level flight. Otter set the power to obtain a slow deceleration rate. A yellow band on the primary flight display airspeed tape warned us of the approaching slow speed condition. After shaker activation I continued to hold aft yoke pressure until the pusher fired. APS conducts this exercise as some pilots have not experienced the pusher fire.
I advanced the thrust levers and lowered the ERJ's nose to recover the aircraft to normal flight conditions.
The high-altitude stall exercise is flown to demonstrate what happens when you slow to the back side of the power curve. The main learning point of this exercise is to lower the nose and accelerate the aircraft out of the stalled condition.
Advancing the power and trying to maintain altitude will not recover the aircraft during this exercise, a marked contrast to the mechanical approach to stall training and evaluation manoeuvre.
The final events in the simulator were several upset recoveries. As in the Extra, Otter placed the aircraft in the desired attitude, and I initiated the recovery when commanded.
The first step in an upset situation is to recognise and confirm the upset. During the first nose-high condition, the standby attitude display indicator (ADI) did not agree with my primary flight display, so I referenced the first officer's display and slowed airspeed to confirm the unusually nose-high attitude.
Using the display as a reference, I used the "say and do" method to employ the AAUR procedure. The last event, a nose-low upset and recovery went smoothly.
Overall, I found using the ADI to execute an upset recovery in the simulator far less daunting than looking out the window at face full of dirt in the Extra.
MULTI-PRONGED APPROACH
In-flight loss of control continues to a leading cause of aviation fatalities. Unlike controlled flight into terrain accidents, technological advances have not dramatically reduced LOC accident rates. While FBW control systems offer some protection, failures and environmental factors can put an aircraft into a life-threatening upset. Improved aircrew training may offer the best prospect for reducing accidents.
For most air carrier pilots, upset recovery training is delivered in academic and practical application sessions in a simulator. Widespread adoption of in-flight training may provide the edge needed to reduce LOC accidents, although in-flight training has risks and is expensive. The four-day course at APS, including computer-based training, Extra 300L flight time and ERJ-145 simulator ride, costs $6,600.
My brief exposure to APS's training programme and visceral in-flight portion in particular, reinvigorated my passion for flight. Seeing an actual in-flight upset and a face full of dirt had more authenticity than the untold numbers of upset recoveries I had practised in full motion simulators.
The industry and regulators should take a close look at in-flight upset recovery training and determine what, if any, role it should play in efforts to reduce loss of control accidents.
Source: Flight International
