Friday, August 23, 2013

Automation vs. Pilots

Airspeed!

Aviation is a young human activity.  The speed at which we progressed from open cockpit bi-planes to our current jetliners does make one marvel at human ingenuity.  Sometimes though I wonder if we are moving so fast that we are forgetting hard lessons learned along the way.  Specifically for this paper I wish to reemphasize the need of pilots to understand the relationship of aircraft control to Angle of Attack and how AoA is affected by pitch attitude and thrust.  Airspeed is an indirect indicator of AoA quality while in normal pitch attitude ranges.  As merely an indirect indicator, there should be no reason for loss of aircraft control and all souls due to pitot-static system failure.






Birgenair Flight 301 (February 6, 1996)
Birgenair Flight 301 was a Boeing 757 who crashed shortly after a night take-off.  This accident was caused by blockage of the number one pitot tube.  The captain’s lack of understanding of how airspeed indication is affected by such a blockage caused numerous decision errors and resulted in total loss of control.  He noticed his airspeed indication was still zero when the first officer called “80 knots” on take-off.  Failing to abort the take-off he then noticed, as they climbed, his ASI was registering again and made the assumption that all was normal and he engaged the auto-pilot to his side of the flight control system.  One of the old lessons hard learned in the days of “steam-gauges” instrumentation was that a typical pitot tube block issue would cause the airspeed indication to increase with altitude increases and to decrease with altitude loss.  This poor lost captain simply engaged his auto-pilot to an airspeed indicator which would keep increasing with the climb until the aircraft reached a dangerously high angle of attack.  This crew noticed the pitch attitude / airspeed discrepancy and discussed it at length, but never saw the core problem.  It is notable that even while the captain was aware of their increasing peril he was reluctant to disengage the auto-flight system.  It seems that he trusted the automation more than himself even while that same automation was obviously malfunctioning.  Adding to the confusion were numerous warnings and alert messages being generated by the ever widening airspeed indication error.  They crashed into the ocean shortly after entering the wing stall regime.


Air France Flight 447 (June 1, 2009)
Air France flight 447 was an Airbus 300 which encountered clouds while cruising in level flight.  This cloud encounter caused some pitot tube ice crystal blockage in one or more of the pitot tubes.  The First Officer, the pilot flying, as the Birgenair captain before him, was confronted with many warnings and alert messages which induced confusion and an unnecessary urge for action, especially since the airspeed error caused the autopilot to disengage.  Unfortunately, his action was to grab the side control stick and sharply pitch up causing a dangerously high angle of attack.  This hapless pilot simply had no idea what he was trying to do.  Rather than simply holding the proper cruise pitch attitude he pulled up into a deep wing stall, which was held the entire three minutes it took to fall to the ocean below.  I have read many articles on this accident wherein writers and industry experts cite the “difficulty” in sorting through all the conflicting signals, warnings, and messages so as to understand this problem and they all make me sick.  How hard is it to see that the pitch attitude is high as hell, thrust is high as hell…aircraft is falling?!  How hard is that?  This is aviation 101.




Northwest Airlines Flight 6231, a Boeing 727, crashed shortly after departing the John F. Kennedy airport on December 1st, 1974.  The National Transportation Safety Board determined that the crew failed to turn on the pitot tube heaters which became blocked by ice crystals causing both airspeed indicators to show erroneous indications.  Almost twenty-two years prior to Birginair 301, this crew misunderstood the "increasing" airspeed indications as they climbed and pitched up into a stall.
   


The Age of EFIS
Our current generation of airline cockpits almost universally has the Electronic Flight Instrument Systems. (EFIS)   These systems integrate and share the raw instrument data so as to provide aircraft status information not only to the visual “instruments” but to other aircraft systems such as engine control computers (Full Authority Digital Engine Control - FADECs), aircraft pressurization systems, autopilots and ground proximity systems, to name just a few.   They also have Flight Directors, which are designed to simplify a pilot’s instrument scan in determining pitch and bank requirements. Rather than interpreting several basic instruments and mentally processing the data so as to determine the required pitch and bank for performance goals, the pilot simply places the aircraft into the attitude displayed by the Flight Director.  The advantage is a simpler scan and a lower mental effort level. Better yet, engage the autopilot to the Flight Director and the airplane does it all!  This is the normal operating mode which the Federal Aviation Agency and virtually every airline have stressed.  Full automation 99% of the time with the pilot hand flying and using basic instruments kept to a barest minimum.  Here is how my airline phrased this concept in our Standard Operating Procedures manual:

Where immediate, decisive, and correct control of aircraft path is required, the lowest level of automation (hand flying without flight director guidance) may be necessary. Such instances would include escape or avoidance maneuvers (except aircraft with flight director windshear guidance) and recovery from upset or unusual attitudes. With the exception of visual approaches and deliberate decisions to maintain flying proficiency, this is essentially a non-normal operation for flight guidance or FMS-generation aircraft. It should be considered a transitory mode used when the pilot perceives the aircraft is not responding to urgent aircraft demands. The pilot can establish a higher level of automation as soon as conditions permit.
Emphasis mine


However, here lies the problem.  The full automation condition is the lowest level of pilot mental engagement and now is prescribed to be the condition wherein our pilots will spend the vast majority of our time.  When the chips fall badly and decisive, correct control inputs are required the pilot is expected to suddenly ramp up his mental and stick & rudder skills to levels of which he has not practiced for a very long time.  Like our poor Birgenair, Northwest and Air France pilots they will find themselves confused and way out of their comfort zones.  They will wish to escape back into the warm and fuzzy world of automation.  I have personally encouraged my First Officers to revert to the basic instrument scan and hand flying for “deliberate decisions to maintain flying proficiency” only to find them very uncomfortable and greatly relieved when they reengaged the autopilot.  Others have hand flown the airplane, albeit with the aid of the Flight Director, for longer than usual following take-off, knowing my reputation of encouraging such behavior.  When they feel they have gone long enough, they engage the autopilot and sit back with a satisfied sigh as if they just completed a long and fruitful workout.  The sad part is those “long” workouts average about seven minutes on take-off and forty-five seconds on landing.

Back in the “steam gauge” days a pitot tube blockage would only effect the airspeed indicator to which it was routed.  However in our new days of automation and systems integration such a blockage causes many warnings in systems areas not typically associated with airspeed.  I believe it this plethora of warnings which are distracting these pilots from the basic task of maintaining aircraft control.  Rather than flying the pitch and thrust first and sorting out the rest, they react to remove the warnings first and forget about basic aircraft operation.


Trans World Express Flight 7604 (December 11, 2000)
Trans World Express Flight 7604 was en route to Greenville, SC on a night flight from St. Louis, MO in an Embraer-145 aircraft.  While climbing to a newly assigned altitude the crew alert system suddenly lit up with numerous messages and warnings.  There were messages announcing failure of all four FADECs.  There were several red messages, many amber messages and some blue ones as well.  There were so many messages on the panel that there was a number presented on the bottom of the screen to let the crew know that they could scroll down to read the extras.  Add to that bells and red lights and you get the idea of how disorienting such an event can be.  The First Officer immediately noticed the FADEC failure messages and said something about losing both engines.  The captain however noted that regardless of all the warnings, the airplane was still flying.  While maintaining a constant pitch attitude and thrust setting it only took him a few seconds to notice that the airspeed indicator on his side was increasing with the climb. With the conclusion that the number one pitot tube was blocked with ice he obtained a clearance from the traffic controller to level off at their present altitude so as to stop the increasing error and to prevent additional warnings from an imminent false over-speed indication.  The First Officer excitedly asked which of the Quick Reference emergency checklists he wanted run, since there were so many to choose from.  The answer to that was not to run any of them because the airplane was flying perfectly and the QRH wouldn’t solve the problem of a blocked pitot tube.  They obtained a descent clearance and the captain noted with satisfaction that the erroneous airspeed indication began decreasing with lower altitudes thus confirming his reasoning.  Soon the ice blockage cleared and all the warning messages disappeared as well.  This flight landed uneventfully.


It Really Is Bi-plane Simple
The new electronic instrumentation and flight control systems are a marvel and they do greatly aid pilots in situational awareness and aircraft control.  However, the downside has been a loss of the basic skills and knowledge which the technology has bridged over.  When the technology fails rather than landing on firm foundational footing, we are finding ourselves falling into a crevasse.  Do not let the startle factor override your basic aircraft control instincts.  Pitch and thrust make the airplane fly, not “airspeed” or quiet alert systems.  Continue to review the basic lessons learned over those past remarkable one hundred years.  Practice basic flying skills, everyday!  Fly safely.

Captain William C. Howe
Trans States Airlines


August 1, 2013

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