Results 1 to 16 of 16

Thread: Flakey airspeed again.

  1. #1
    Join Date
    Jul 2003
    Posts
    4,330

    Flakey airspeed again.

    Another air tragedy due to faulty pitot tubes it seems. A bit much surely!

  2. #2
    Join Date
    Aug 2005
    Location
    NEOTP Atlanta, GA
    Posts
    2,372
    It's a bit early to declare plugged pitot tubes as the root cause of the Lion Air flight. But, yeah, those critical components are culprits. In the case of Air France 447 the pitot tubes were blocked by ice. That's almost impossible in the the Lion Air case.

  3. #3
    Join Date
    Jun 2004
    Location
    The Great NorthWet
    Posts
    13,668
    Linky, others available with a Google. Upsetting. This wasn't my area of expertise at Boeing, but I still got involved once in a while with issues. Just off the top of my head, it seems like GPS could at least be used to indicate something might be awry and alert the pilots. It can't, of course, be the primary indication as it doesn't account for wind.
    I also wonder to what extent the system differs on the 737Max from earlier ones.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  4. #4
    Join Date
    Aug 2005
    Location
    NEOTP Atlanta, GA
    Posts
    2,372
    From the earlier problems with that plane there was an issue where the airspeed indicators did not agree; the pilot in command saw one set of numbers, the co-pilot saw another. Supposedly the problem was corrected before the fatal flight.

    The problem with AF447 - and possibly this flight - is that the unreliable data caused confusion in the cockpit. In AF447 one of the pilots pulled back on the controls to increase the angle of ascent yet the stall alarm was going off. The other pilot was trying to push the nose down. It's almost as if they had forgotten how to fly a dang plane. From Wikipedia:

    While the inconsistent airspeed data caused the disengagement of the autopilot, the reason the pilots lost control of the aircraft remains something of a mystery, in particular because pilots would normally try to lower the nose in the event of a stall.[208][209][210] Multiple sensors provide the pitch (attitude) information and there was no indication that any of them were malfunctioning.[211] One factor may be that since the A330 does not normally accept control inputs that would cause a stall, the pilots were unaware that a stall could happen when the aircraft switched to an alternate mode due to failure of the airspeed indication.[207][i]
    For a while now there has been concern in the pilot community and the safety boards that commercial airlines are training pilots to fly systems and not aircraft; in effect, the pilots can play the video game but have forgotten how to fly in the real world. They have become too dependent on the automation.

  5. #5
    Join Date
    Jun 2004
    Location
    The Great NorthWet
    Posts
    13,668
    Conflicting pilot controls are a bit of an issue, for me at least, with the Airbus passive joystick system. The pilots get no feedback as to what the other guy - or the autopilot - is doing. The airplane basically adds the two inputs together. The good ol' mechanically linked wheel and column on a Boeing provides visible and tactile feedback. That said, FBW airbuses have flown millions and millions of miles, nearly all of it safely.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  6. #6
    Join Date
    Sep 2004
    Posts
    15,036
    And the pilots would hear an audible warning about the dual inputs given.

    Care should be taken to jump to the "forgotten how to fly a plane due to autopilot" conclusion. Many accidents predating autopilot show that it is not uncommon that pilot and copilot are distracted by a situation (medical emergency, smoke in the cockpit, strange sensor readings) and focus so much on that issue that they forget their number one priority, which is keeping the aircraft under control. It can get quite extreme. There are multiple examples (also from many decades ago) where all the warnings of a stall situation are ignored/switched off/counteracted because their train of thought excludes the possibility of an actual stall; all the attention goes to solving the annoying "false" alarms or whatever other problem they (think they) have. With multiple examples where pilots are confused by stall warnings, and nobody bothers to do the safe thing = putting the plane in a flat, level attitude. So it's more about "forgetting to fly the plane" rather than "forgetting how to fly the plane".

    I've spent quite some time on these situations during my studies, including making a simulation of the Trident crash. So when I was in a hot air balloon and one of the passengers had a medical emergency, I kept an eye on the pilot (captain? commandeer? Overlord?) to make sure he remained focused on flying (sailing? floating? levitating?) the thing. He did and all ended well.

  7. #7
    Join Date
    Aug 2005
    Location
    NEOTP Atlanta, GA
    Posts
    2,372
    Yes, better to say “focus on the flying”and recall the old adage:
    Aviate
    Navigate
    Communicate

    In that order.


    Sent from my iPhone using Tapatalk Pro

  8. #8
    Join Date
    May 2008
    Location
    The Netherlands
    Posts
    14,874
    Lion Air flight JT 610. Putting the flight number in for future search, ie when a full report is published in a year or two.

    Quote Originally Posted by schlaugh View Post
    It's a bit early to declare plugged pitot tubes as the root cause of the Lion Air flight.
    Yeah. If the reports are right that the failure happened on several earlier flights, that might on one hand indicate stupidity, lazyness, costcutting on maintenance and what have you, but on the other hand it might also be an indication that the mentioned fault wasn't as bad as suggested, and no reason to ground the plane or repair immediately.
    ____________
    "Dumb all over, a little ugly on the side." -- Frank Zappa
    "Your right to hold an opinion is not being contested. Your expectation that it be taken seriously is." -- Jason Thompson
    "This is really very simple, but unfortunately it's very complicated." -- publius

    Moderator comments in this color | Get moderator attention using the lower left icon:
    Recommended reading: Forum Rules * Forum FAQs * Conspiracy Theory Advice * Alternate Theory Advocates Advice

  9. #9
    Join Date
    Jul 2003
    Posts
    4,330
    Two points occur to me and I am far removed from any connection to aviation. First the engineering of the pitot tubes and associated gear must be very advanced after decades of development. They have to cope with rain and dust so do they have equipment "blow" out any obstructions. Second there must have been occasions when pilots have realised the airspeed indication is faulty but they managed to cope and get down safely. These recent accidents including the Russian tragedy seem to show a loss of experience.

  10. #10
    Join Date
    May 2008
    Location
    The Netherlands
    Posts
    14,874
    According to an aviation news site there was a directive from Boeing concering an Angle of Attack (AOA) sensor (referencing twitter https://mobile.twitter.com/AvGeekJam...340096/photo/1 ). AFAIK that has nothing to do with pitot-tubes, but of course the one does not necessarily exclude the other.
    ____________
    "Dumb all over, a little ugly on the side." -- Frank Zappa
    "Your right to hold an opinion is not being contested. Your expectation that it be taken seriously is." -- Jason Thompson
    "This is really very simple, but unfortunately it's very complicated." -- publius

    Moderator comments in this color | Get moderator attention using the lower left icon:
    Recommended reading: Forum Rules * Forum FAQs * Conspiracy Theory Advice * Alternate Theory Advocates Advice

  11. #11
    Join Date
    Aug 2005
    Location
    NEOTP Atlanta, GA
    Posts
    2,372
    The FAA and Boeing are saying that erroneous AOA inputs will cause the nose to automatically pitch down because the system thinks the plane is stalling, or about to. The directive is to shut off the automatic trim and fly the plane manually.

    From a Forbes story on the directive:

    The accident and the FAA warning, which comes after Boeing issued a similar bulletin, may be less an indication that there’s anything wrong with the new version of Boeing’s top-selling plane than of how increasingly automated flight systems erode pilot skills, says Keith Mackey, a Florida-based safety consultant who’s a former airline pilot and accident investigator.

    To put it simply, says Mackey, the FAA’s directive tells pilots to turn off the autopilot, and if necessary the pitch trim system too, and fly the plane yourself.
    https://www.forbes.com/sites/jeremyb.../#2616b00d4847


    Sent from my iPhone using Tapatalk Pro

  12. #12
    Join Date
    Dec 2007
    Location
    Bend, Oregon
    Posts
    6,041
    I know little about aviation instrumentation but I do know something about pitot and other air speed instruments (they're used in nuclear power plants). I wonder, would it be a good idea to have a backup pitot assembly housed within the fuselage, ready to mechanically deploy in the event the primary sensor(s) is suspected of being iced or otherwise fouled? Being housed, it would be out of the elements until it's deployed. Mind you, I'm one of those folks that believes with sophisticated systems such as aircraft (and nuclear plants) that a lot of smart people have already had their hand in designing the things so I imagine this idea has already been kicked around and dismissed.

  13. #13
    Join Date
    Jun 2004
    Location
    The Great NorthWet
    Posts
    13,668
    Commercial airplanes already have three pitot probes and two AOA sensors. One pitot probe is displayed for the Captain, a second for the First Officer, and a third feeds a standby instrument that has an independent battery power supply and works even in case of a "black cockpit". That SHOULD cover everything. Unless someone has covered them with tape while the aircraft is being painted and forgotten to remove it. That cause a 757 to crash one time.

    What surprises me a little is the statement that the airplane responds to a sensed impending stall by putting itself into a dive. I don't recall Boeing's aircraft doing that. Mostly they just have a "stick shaker", which vibrates the control column and makes a considerable noise while doing so to alert the pilots. However, I'm less familiar with the 737 than some other models, especially in the pitch control system. Perhaps it has a "stick pusher" as well.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  14. #14
    Join Date
    Sep 2004
    Posts
    15,036
    Stick shaker/pusher already was on the Trident. Not saying modern Boeings have it, not sure about that, but it's been around for half a century.

  15. #15
    Join Date
    Jun 2004
    Location
    The Great NorthWet
    Posts
    13,668
    Oh, absolutely, nothing new there. I just wasn't aware of modern Boeing's using a pusher. Now that I think about it, perhaps the stall warning system is simply connected to the autopilot. That makes more sense.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  16. #16
    Join Date
    Jan 2004
    Location
    No longer near Grover's Mill
    Posts
    4,606
    From news reports, it sounds like the pilots didn’t know the plane had a pusher.


    Sent from my iPhone using Tapatalk
    I may have many faults, but being wrong ain't one of them. - Jimmy Hoffa

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •