A basic summary of the tragedy of Air France Flight 447 can be read here. Bottom line is that an Airbus 330 crashed into the Atlantic Ocean on June 1, 2009, killing all 228 aboard. For two years, experts and amateurs alike speculated on what could cause a modern jetliner to plunge 35,000 feet into the ocean. Speculation centered around intense thunderstorms in the area. Telemetry indicated that the airspeed indications were erratic, then the autopilot and auto-throttles disengaged. Telemetry cut off at that point, but didn’t indicate anything catastrophic before they went silent. The crew made no radio transmissions – no emergency call, no mayday, nothing. One Airbus 330 disappeared silently into the sea with 228 on board. The mystery defied solution…until now.
At the beginning of May of this year, the data recorder and cockpit voice recorder were recovered from the bottom of the Atlantic. Although two years of salt water and tremendous pressure took their toll, their internal data survived. The tale that they apparently tell resolves the mystery, but multiplies the tragedy.
It seems that the heated pitot tubes which provide the air pressure inputs to the air data computer, producing the airspeed indication, iced over. That caused the airspeed indication to become erroneous and fail. Having lost that key input from the air data computer, the autopilot and auto-throttles disengaged, requiring the pilots to fly the aircraft by hand. In what is designed as a safety feature, the stall warning system activated because the airspeed indication, now low and maybe even zero if the pitot tubes were totally blocked, was below stall speed. In that condition, the stall warning would not have shut off until its circuit breaker was pulled. Nothing the airplane itself did would have terminated the stall warning at that point.
Stall speed is that speed for a given weight and configuration at which the wings no longer produce more lift than the aircraft weighs and the aircraft descends under the ever-present influence of gravity. The correct recovery procedure requires lowering the aircraft nose to regain airspeed so the aircraft will again be able to fly. Sadly, the crew didn’t do this. For modern transport aircraft, actually just taking your hands off of the controls will allow the aircraft to recover all by itself. They didn’t do that, either.
Actually, the recovery maneuver wasn’t required anyway. Although the airspeed indication failed, the aircraft was still flying just fine. You don’t need an airspeed indicator to fly, although it’s a nice convenience. Let me explain.
Early in pilot training, we were taught that there are essentially three categories of instruments, which include control instruments and performance instruments. Control instruments are directly contolled by the pilot, hence the name. They include aircraft attitude (pitch & roll) and power indications like RPM and manifold pressure for a reciprocating engine and engine pressure ration or one of various engine speeds (usually the first fan and/or compressor stage speed for a turbofan like the A330 has) for a jet engine. Performance instruments measure and present the effect of what the pilot did with the controls, such as airspeed, vertical velocity, and altitude. At a given altitude, weight, and configuration for a particular aircraft, setting the pitch and power appropriately will always result in a given airspeed. (Actually, the angle of attack is the key underlying factor here, but since non-aviators reading this won’t readily latch onto the concept, I’ll stick to airspeed here.) You set the controls and the performance instruments merely confirm the outcome. Or put another way:
Although this is emphasized in instrument flying, it actually lies at the core of basic airmanship. In visual conditions, God’s great horizon provides your attitude information rather than an instrument display in the aircraft. That’s Flying 101 in a nutshell.
One other key indicator to verify the correct pitch and power settings is sound. As an aircraft increases in speed, the wind noise over the cockpit increases significantly. A good pilot uses these cues almost subconsciously to confirm his/her current situation. Aircraft can buffet or shake at low speed due to an approaching stall and at high speed due to Mach buffet. If one had no other indications, perhaps losing airspeed, vertical velocity, altitude, the horizon, and all warning horns, you can tell whether you are in stall or Mach buffet simply by listening to the wind over the cockpit. If it’s relatively quiet, you’re approaching a stall. If it’s noisy as heck, you’re in Mach buffet. Simple and effective. Again, basic airmanship.
Given all that background, one has to conclude that when the airspeed indication failed and the autopilot and auto-throttles disengaged, the A330 was in the heart of its flying envelope. Remember that they were comfortably cruising at the time. The crew had to do nothing more than ignore the obviously incorrect airspeed indications and warning horns while setting a well-known cruise power setting on their engine instruments and appropriate pitch on their attitude display. That’s it – mission accomplished. They could have flown all the way to Paris that way, but more than likely the ice would have sublimated off of the heated pitot tubes shortly after clearing the weather. Even more tragic, the crew probably could have done absolutely nothing at all and everything would have been fine.
Tragically, that’s not what the aircrew of Flight 447 did. Instead, they chose to believe the erroneous performance instruments and warning indicators apparently without cross-checking their primary control instruments. Even worse, they did exactly the opposite of what’s required to recover from a stall and raised the nose of the aircraft, climbing 3,000 feet and actually causing the A330 to stall. The aircraft dutifully obeyed their commands and basically quit flying, eventually impacting the ocean because for the last 4 minutes or so the crew never recognized or corrected their mistake.
While not everything that happened during the A330’s tragic descent to the sea is clear as of this writing, it is painfully clear to me that 228 people died for nothing. A crew caused a perfectly flyable aircraft to plunge down through 38,000 feet of air in less than 4 minutes, ending in disaster due to the oldest “accident” cause across time – human error.
Which takes us back to the lessons that all aviators should take from this tragedy. There’s nothing new here:
1. Get back to basics. Good airmanship never goes out of style and should be the daily concern of every aviator. Probably the best book on flying and airmanship I’ve ever read was Stick and Rudder: An Explanation of the Art of Flying by Wolfgang Langewiesche. Written in 1944, it revolutionized flight instruction. You can find a couple of pages of notes explaining the very few differences with modern approaches to flying here. Read it, learn it, live it.
2. Deliberately reacquaint yourself with the basics during periodic refresher training. Having been through 30+ years of refresher training, I observe that they tend not to emphasize the basics. Beyond the usual engine and system malfunctions, try covering up the airspeed indication and then fly some level flight and an approach. Learn your airplane – its feel and sounds, including the engine sounds at key flight conditions. The crew of United Airlines Flight 232 landed their crippled DC-10 through solid airmanship and great crew coordination.
3. Learn to fly the aircraft, not just operate the equipment. Modern aircraft have a host of complex avionics and computer interfaces, which take significant training to master. However, the avionics rarely kill anyone. Failure to fly the aircraft, though, inevitably proves fatal. Captain Chesley “Sully” Sullenberger deftly ditched US Airways Flight 1549 in the Hudson saving all aboard with no help from any avionics or computers.
4. Listen to your aircraft. Airplanes are always talking to you – either through the instruments, vibrations in the structure, wind noise, smells, sounds, etc. Are you listening? We should all be asking ourselves what the aircraft telling us. Something doesn’t sound, feel, smell, etc., right? Track it down. Avoid complacency.
5. Aviate, navigate, communicate – in that order. Fly the aircraft – first, last, and always. If you’re not mastering the machine, it hardly matters where you’re going and what you’re saying. Sound too simplistic? Not if you remember that Eastern Airlines Flight 401 flew down into the Everglades killing 101 people because the crew’s attention was centered on a light bulb in the cockpit.
6. The first step in every emergency is to wind the clock. Wind the clock, you ask? Yes. We were taught this in USAF pilot training and it’s every bit as important in all spheres of flying. Wind the clock while you’re thinking about the situation for a few seconds…before doing something possibly irreversible. Wind and think – what’s really happening and how can I confirm it? If you don’t have a windable clock, pretend. A few seconds of analysis before snatching the aircraft’s nose up and holding it there just may have saved 228 people on June 1, 2009.
I could go on, but this post is long enough. Tragedy can be avoided. Now get out there and be one with your aircraft. To paraphrase Ty Webb from Caddyshack, “See the airplane…be, be the airplane.”
Fly smart and fly safe!