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  • #16
    Originally posted by Evan View Post
    The extreme uncommanded roll beyond 70° brought on the (accelerated?) stall.
    Interesting cause & effect there...
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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    • #17
      Originally posted by Gabriel View Post
      And you are discussing if the problem was the sudden addition of power or the stall recovery?
      Yes, because this shouldn't just be about 'these guys'. There are going to be guys like this continuing unstable approaches, suffering from continuation bias and landing successfully over and over again, until they don't. You don't have to be ok with that to accept it. I'm not ok with it but I have accepted that it is going to persist.

      But steps can be taken to assure that a piston-twin pilot transitioning to a high-performance t-prop KNOWS the correct go-around and approach-to-stall procedures, KNOWS the reasons for them and DEMONSTRATES proficiency on them before getting that certification. As 3WE pointed out, the MU-2 had a nasty reputation early on because pilots were not being properly trained on the vital differences between piston procedure and t-prop operation. Examples:

      Because the MU-2 offers very high performance at a relatively low cost, some of its operators lack sufficient training and experience for such an advanced aircraft. The MU-2 has performance similar to a small jet, yet early pilot certification required only a simple endorsement from pilot certificates for much slower twin piston-engine aircraft. The fact that numerous MU-2 pilots were inexperienced at high speeds and high altitudes seems to have resulted in the high crash rate. Once type-specific training was required for MU-2 pilots, the accident rate dropped to normal levels.

      Some fatal accidents have occurred because normal engine-out procedures for light twin aircraft are not effective when flying the MU-2. The commonly taught procedure of reducing flap following an engine failure on take off leads to a critical reduction in lift in the MU-2 due to the highly effective double-slotted flaps. When pilots were taught to retain take-off flap and to reduce climb rate in the event of an engine failure, MU-2 accident rates were reduced to almost nil.
      Steps were taken in 2008:

      In early 2008, the FAA issued a Special Federal Air Regulation (SFAR) directed at MU-2B operations. Pilots flying this aircraft after that date (current MU-2 pilots would have a year to come into compliance) were required to receive type-specific initial training, as well as recurrent training. The agency also required that a fully functional autopilot be available for single-pilot operations, and that FAA-approved checklists and operating manuals be on board at all times. Unusual for this SFAR, pilot experience in other aircraft types cannot be used to comply with MU-2 operational requirements. For instance, the requirement to perform landings within the preceding 90 calendar days before carrying passengers is altered by this SFAR to require those landings be made in the MU-2.
      Yet, this pilot didn't seem to have an essential understanding of throttle handling as low airspeed. So something is broken there.

      The industry can and should continue all efforts to impress the requirement for stable approach criteria. But that cannot preclude giving pilots the knowledge they need to save themselves (and their passengers) from themselves when they fall prey to human factors. Or should we just eliminate stall warnings and procedures altogether and rely on perfect airmanship at all times?

      Comment


      • #18
        Originally posted by Evan View Post
        Yes, Schwartz, from the moment the throttles were firewalled, which caused the upset. From that point on (allowing a second or two for reaction time), I'm not sure anything could have been done to save them. Pulling back the throttles along with leveling the wings maybe, but with less than 500ft to regain lift and arrest descent, I don't think so. At best perhaps a less violent crash.
        Yeah, the report indicates the pilot did everything correctly to right the aircraft and it hit the ground almost level, nose up a bit. The aircraft bounced once (uphill) and then skidded. It sounds like the pilot did indeed correct the upset properly, but didn't have enough altitude left and that once the upset happened to that degree it was over at that altitude. Reading the report, I came away that they implied he could have advanced the throttles quickly had he been prepared for the response of the aircraft. They implied he wasn't practiced enough on that aircraft and was caught by surprise which means to me, he knew what to do once it happened, but there was a delay in response due to surprise. I think he had very little margin for error at that altitude and airspeed.

        On final approach, the aircraft slowed to within a few knots of the stall speed before this was recognized by the pilot. The sudden addition of high power at low airspeed in the MU-2B produces a right-rolling tendency, which can lead to loss of control if not anticipated and corrected. The pilot was surprised by the right roll and delayed correcting it, which permitted the aircraft to roll more than 70° before returning to a near wings-level attitude at impact. A loss of control occurred when the pilot rapidly added full power at low airspeed while at low altitude, which caused a power-induced upset and resulted in the aircraft rolling sharply to the right and descending rapidly.

        Although information was available to explain the aircraft's characteristics when high power is applied at low airspeeds, it is unlikely that the pilot was familiar with this situation, based on his reaction during the occurrence. The pilot had about 2500 total flight hours and had held an airline transport pilot licence for about 6 years, but his flying experience was primarily on non–high performance single-engine and multi-engine aircraft. During the 20 months that the pilot had flown the occurrence aircraft, he had accumulated about 125 flight hours, of which at least 100 hours were flown under the supervision of a qualified and experienced pilot. In the previous 3 months, he had logged only about 19 flight hours and, in the previous 30 days, only 4 flight hours. The investigation could not determine how many pilot-in-command (PIC) hours the pilot had flown with another pilot accompanying him.


        It is interesting that someone had installed a light weight video/audio recorder which is how they were able to do such a good analysis.

        The data and audio retrieved from the Wi-Flight was critical to understanding the events that led to the accident. Although not required by regulation, the installation and use of a lightweight flight recording system during the occurrence flight, as well as the successful retrieval of its data during the investigation, permitted a greater understanding of this accident.

        During the approach to Runway 07, the aircraft struck the base of a hill in a left-wing-low, nose-high attitude, 1.4 nm west and 1000 feet south of the runway centreline (Figure 4). The aircraft momentarily became airborne again, then struck the ground and slid for about 100 feet before coming to rest.

        Propeller strikes were found in the ground on both sides of the initial impact site: 3 strikes on the left side and 2 on the right side. Measurements of these strikes indicated that the engines were driving both propellers and producing power at impact. Based on the analysis of the propeller strikes and the flight data, the investigation determined that the aircraft struck the ground at a ground speed of about 100 knots and a descent rate of approximately 4000 fpm.


        Unfortunately, the descent rate was too fast to be survivable even thought the aircraft appears to have protected the occupants.

        The aircraft had 2 distinct ground impacts. The investigation calculated the peak vertical acceleration, which was reached during the first impact, to be about 78g for 0.06 seconds. Research has established that a vertical g force of this magnitude causes severe injuries even if the aircraft structure and restraints provide maximum attenuation of impact forces.Footnote 39

        All occupants had been wearing the available seatbelts.

        Comment


        • #19
          Originally posted by Schwartz View Post
          Reading the report, I came away that they implied he could have advanced the throttles quickly had he been prepared for the response of the aircraft.
          I'm not so sure about that. At minimal airspeed those wing spoilers might lack the authority to overcome so much torque-induced roll, so even a well-prepared pilot might get into some roll excursion when firewalling the throttles at that speed. I suspect the low-energy recovery procedure involves advancing the levers more carefully AND being prepared to counter the roll it might cause.

          Comment


          • #20
            Superior pilots use their superior judgement to avoid using their superior flying skills.

            I agree with 3WE that a pilot that had been so sloppy and doesn't know its airspeed and altitude and is sitting 2 miles behind the airplane he's flying will doubtfully suddenly recover all his wits the moment that the fit hits the sham. If the pilot had the proper training and attitude he would not have been in that position to begin with, and if he is then he doesn't have the proper training, knowledge or attitude, so again, it is unlikely that he will react brilliantly to the upset (physical after the yaw/roll or "psychological" the moment that the stick shaker shakes).

            That said, Evan, you also are right in one thing (that you don;t even mention, but it is there hidden in what you said, even if you don't know it). But first some background.

            First of all, you don't need to evangelize me on the problems and importance of correct low speed management (not that you are trying). My "stall rant" thread is the main document that the FAA and EASA and the aviation industry at great reverted to when they designed the new stall and approach to stall recovery principles (not really, but my "document" came first, and is still better than the industry's).

            2nd, the reason why the MU is better than aileron-fitted planes in stall is mainly because the spoilers don't have adverse yaw (that couples into adverse roll with the dihedral effect) so precise rudder coordination is less critical. Neither ailerons or spoilers are effective if that portion of the wing is stalled (spoilers basically stall part of the wing, so doing that in a stalled part will hardly have any effect), and all planes are designed so as the root of the wings stall first so in incipient stall the tips (and the ailerons or spoilers in the MU) remain unstalled. Another problem with ailerons is that, at a critical point, a down-going aileron can promote a stall in that part of the wing that you are truing to push up, with a net reduction of lift in that zone and hence adverse roll. That's why the new standards based on my paper call for first unloading the wing (euphemism for reduce the angle of attack) before rolling wings level. But the reduction of effectiveness of the roll control surface due to reduced speed and increased AoA as well as the almost elimination of the roll damping (main component in roll stability) is common to aileron and spoilers. So the advise to reduce AoA FIRST and level wings first is till, well, advisable.

            Talking from a "generic skills common sense" and not MU specific procedures or characteristics, the moment the pilot had the stickshaker he should have reduced AoA FIRST (and we are talking about a split-second first). Then the roll due to addition of torque would have been reduced somehow by the improved roll damping and the spoilers would have been more effective to control roll. We will never know what happened up there, but I suspect that when this pilot saw the nose going down he freaked out and pulled up, and that the plane had more that a stickshaker but rather a real stall at some point. Was the plane still recoverable after the initial roll upset caused by the sudden addition of power 1 knot above the official stall speed? Almost sure yes, with a near-perfect use of stick and rudder that no pilot is likely to pull out at that point.

            None of the above is MU specific, and is all very important. Regarding the MU specific or "high performance twin turboprops" specifics, the sudden yaw and roll caused by the sudden addition of power, this is also a known situation in high-power piston singles and everything in the middle.

            After flying planes like the Cessna 152 and the Piper Tomahawk with 112 HP, one day I flew (with an instructor of course) a 230 HP Cessna 182. Because we had taken off from a somehow busy airport, we went to practice touch-and-goes in a nearby 600m-long grass field. IT was my first time in a plane with constant-speed propeller and (spoiler alert) rudder trim (why would you want a rudder trim in a single?). I was impressed with my own performance managing the throttle, RPM, airspeed, flaps and descent path towards the landing. Touch (with the stall warning just starting to sound).. and go!!! And there does the nose go to the left. It took me completely by surprise. The plane yawed waaaay to the left and was rolling too. I quickly reacted both with rudder and aileron inputs. The aileron inputs were effective (much similar reaction than say a Cessna 152) but the rudder didn't seem to do much. Of course, it was me who was not doing much. Suddenly I felt the the rudder pedal have an "automatic" input that felt like all the way to the right (it was not), something that I would have never dreamed of doing in the Tomahawk unless unless I was doing an agressive sideslip. Of course, it was the instructor. Then I said to the instructor "oh, so that's what the rudder was there for". Next landing was equally perfect but its subsequent go around was quite better, but I was still shy on the rudder. There is a very nice video out there in YouTube where you have a Cessna 1820 doing a touch and go in a dirt runway and the moment that they apply power and go up the plane yaws like 20 degrees to the left and the people on the ground starts to scream "right rudder, right rudder!!!", it was very similar to what happened to me.
            Consider that we are much more sensible to roll than yaw. In VMC we are naturally much better at keeping the wings level than the ball centered. That explains why in my case and in the video there was no significant roll. In IMC, however, it is possible that the roll takes more time to identify and hence the correction is delayed. Probably this was a factor too.

            So, you are right, adding sudden power in a high-power propeller airplane is problematic, but it is not something exclusive of the MU or "high performance turboprops".

            Now going back to the part that I agree with what you didn't say "There is no "engine stall recovery during go around" procedure. Procedures, especially abnormal or emergency procedures, typically assume that you have ONE problem. And that is a problem because, sometimes, the problem X that you are reacting too was triggered by by a predeceasing problem Y that has an influence on how you need to react to problem X.

            The go-around on the 737 goes something like arrest descent, TOGA, flaps 15, with positive climb gear up.
            Following exactly that procedure almost killed everybody.

            There were an incident in a 737, that could have easily been a tragedy, where the AT had a failure and kept the throttles retarded while the AP kept the glide slope in a deteriorating speed trend (very much Turkish style). The pilots eventually noted that the speed was WAAAAY below Vref and called go-around, arrest descent, TOGA, flaps 15, which immediately triggered the stickshaker. The pilot applied nose-down input to the stops and the airplane's speed did increase first, but the plane kept pitching up, and up, and up, against the full nose-down input, until it eventually fully stalled (despite the TOGA), the nose dropped and the plane started to fall. During the fall the airspeed increased enough that the elevator gained more authority and finally, they were able to recover from the stall, arrest the descent and climb, but the plane started to pitch up uncontrollably again and at that point they had the clarity of mind to apply nose-down trim, which finally allowed a full recovery of normal flight.

            There SHOULD BE (but there isn't) and the pilots SHOULD BE trained for (but they aren't) procedures for go-around that are sensitive to the reason that originated the go-around. If you are in a very slow speed situation, arresting the descent, selecting flaps 15 and applying TOGA are all very bad ideas. Better apply some intermediate thrust (climb?), keep descending, let the speed recover to Vref, and then execute the "normal" go-around.

            It is very possible that, in the MU, pilots are trained to execute a go-around applying full thrust quickly. And it is possible that this is not a big issue if you are flying at the approach speed of 125 knots, or "never below 120" (as the pilot himself was recorded saying, and as he asked the other pilot to keep an eye on the ASI to ensure), but when you are flying 1 knot above stall, the situation can be different. At 120 knots you have 40% more dynamic pressure than at 100 kts, which means 40% more effective fin in yaw damping and anti-yaw moment that will reduce the natural yaw on the same asymmetric thrust (even without using the rudder), the rudder will be more effective, the wings will have more roll damping (even without using the roll spoilers, because of the higher speed but also the lower AoA), the roll spoilers will be more effective, the thrust (and hence the asymmetric thrust) will be lower, and the P-factor will be lower both due to the lower AoA and the lower thrust. So 120 vs 100 are two total different animals (totally different plan e behaviors). And I doubt very much that there is "go-around when you are 1 knot above stall speed" procedure in the MU (or any other plane). And there should? How many combinations of factors are you going to procedurize and train for? n! grows VERY quickly (more than exponentially quickly) as n increases.

            Now, good airmanship dictates that preservation of AoA is priority one in ANY situation, NOTHING goes first other than that, under NO circumstances. Airspeed/energy comes as a close second (in part because it is so related with AoA). So, both in the 737 incident and in the MU accident the pilots should have first controlled the AoA and speed and then execute the go-around, or at least execute the go around while minding the AoA and speed as first priority over climbing (and airspeed is not increased only with thrust but with pitch, since simply adding thrust will have only a temporary and non-sustainable airspeed gain (see the 737 incident above). But yes, you need to teach, learn and practice these things. That are NOT MU specific. And I am not neglecting the importance of knowing your plane and its behaviors, but trying to rescue (from you) the importance of good general understanding, theoretical and practical, of these concepts independently of the airplane type).

            (Again, "watch your speed, especially in an approach in IMC" and "establish a stabilized approach gate" would have worked much better than all that: Superior pilots use their superior judgement to avoid using their superior flying skills.)

            --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
            --- Defend what you say with arguments, not by imposing your credentials ---

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            • #21
              Yet, this pilot didn't seem to have an essential understanding of throttle handling at low airspeed stall. So something is broken there.
              Fixed, agreed, and no, it is not a MU or "high-performance twin turboprop" thing.

              --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
              --- Defend what you say with arguments, not by imposing your credentials ---

              Comment


              • #22
                Yeah, the report indicates the pilot did everything correctly to right the aircraft and it hit the ground almost level, nose up a bit.
                I am not so sure. The clephone-bassed recorded measured 3D Gs and attitude (and it seems that airspeed too, somehow?), but not control inputs and AoA. I think it is very likely that the pilot actively stalled the plane by pulling up and crashed in a stall (yes, wings level and nose up). We will never know.

                --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                --- Defend what you say with arguments, not by imposing your credentials ---

                Comment


                • #23
                  Originally posted by Gabriel View Post
                  Superior pilots use their superior judgement to avoid using their superior flying skills.
                  Gabe, This is the most profound thing I have ever seen you write. I don't know if it's yours, but I love it, and I plan on using it!

                  Comment


                  • #24
                    Originally posted by Evan View Post
                    I'm not so sure about that. At minimal airspeed those wing spoilers might lack the authority to overcome so much torque-induced roll, so even a well-prepared pilot might get into some roll excursion when firewalling the throttles at that speed. I suspect the low-energy recovery procedure involves advancing the levers more carefully AND being prepared to counter the roll it might cause.
                    Per the report, they seemed pretty definitive. They clearly imply the roll should have been controllable had it been anticipated or even reacted to quicker.

                    On final approach, the aircraft slowed to within a few knots of the stall speed before this was recognized by the pilot. The sudden addition of high power at low airspeed in the MU-2B produces a right-rolling tendency, which can lead to loss of control if not anticipated and corrected. The pilot was surprised by the right roll and delayed correcting it, which permitted the aircraft to roll more than 70° before returning to a near wings-level attitude at impact. A loss of control occurred when the pilot rapidly added full power at low airspeed while at low altitude, which caused a power-induced upset and resulted in the aircraft rolling sharply to the right and descending rapidly.

                    Comment


                    • #25
                      Originally posted by BoeingBobby View Post
                      Gabe, This is the most profound thing I have ever seen you write. I don't know if it's yours, but I love it, and I plan on using it!
                      If it's mine? I can't believe you've never heard it. It's as old as "height and speed help keep your teeth" (oh, wait, you've never heard that one either, right?)

                      * Ok, the last one is popular among Spanish speaking pilots "Velocidad y altura conservan la dentadura", which rhymes, and my free translation to English that is quite literal rhymes too. But the one about superior plots I've seen it written in many different forums, aviation magazines, aviation websites, always in English. Like "aviate, navigate, communicate" or "the three most useless things in aviation, the altitude above, the runway behind, and the ullage in the tanks" or "take-off is optional, landing is mandatory" or "better being in the hangar sorry for not going flying that being in the air sorry for not staying in the hangar".

                      --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                      --- Defend what you say with arguments, not by imposing your credentials ---

                      Comment


                      • #26
                        Originally posted by Gabriel View Post
                        I am not so sure. The clephone-bassed recorded measured 3D Gs and attitude (and it seems that airspeed too, somehow?), but not control inputs and AoA. I think it is very likely that the pilot actively stalled the plane by pulling up and crashed in a stall (yes, wings level and nose up). We will never know.
                        Maybe.

                        Immediately following the power application, the aircraft experienced an upset, yawed, and quickly rolled to the right, exceeding a 70° angle of bank, and then rapidly descended. The pilot was caught by surprise and reacted by trying to counteract these conditions. At approximately 150 feet AGL, the aircraft regained a wings-level attitude. However, the aircraft was still descending at a high rate and had not regained the loss of altitude resulting from the upset. During this time, the aircraft's rate of descent increased from 1350 fpm, reaching a maximum of 4600 fpm. There was insufficient altitude to recover the aircraft.
                        They don't really spell out the details of what the pilot tried to do to recover the bank and rapid descent. I would think though if he performed wrong or ineffective measures they would have called it out?

                        Further down in the report this is interesting and perhaps related to what you wrote about earlier:
                        1.18.6 Stall recovery / approach to stall recovery
                        The original SFAR No. 108 training for stall recovery required the following actions to be carried out simultaneously:

                        apply max power;
                        adjust pitch as necessary to minimize altitude loss; and
                        level wings if in a bank.
                        In 2012, the FAA revised its stall recognition and recovery procedures for all aircraft and all training programs. The new procedures emphasized establishing a positive reduction in AOA by pitching the aircraft's nose down to re-establish smooth airflow over the wings. This procedural change made it less likely that pilots would encounter a secondary stall while trying to minimize altitude loss. The new procedure also stated that some altitude loss must be accepted to ensure a good safety margin during the recovery.

                        The new stall recovery procedures include the following instructions:

                        disconnect the autopilot;
                        reduce the AOA;
                        level wings if in a bank; and
                        add power.
                        The SFAR No. 108's stall recovery method was amended to be consistent with the FAA's new stall recovery procedures. Since 2012, the revised stall recovery methods have been required to be demonstrated when pilots complete the SFAR No. 108 training.

                        In the MU-2B, when the new stall recovery procedures are used, about 450 feet of altitude loss can be expected during the recovery from a wings-level power-off stall. About 200 feet of altitude loss can be expected during the recovery from a wings-level power-on stall.
                        The aircraft upset just shy of 500ft, and the pilot reacted slowly likely leaving him less than 450 ft to recover in that aircraft. The sad irony is he would have been better off in a wings level stall as he had enough altitude to recover from that.

                        Comment


                        • #27
                          Originally posted by Gabriel View Post
                          Superior pilots use their superior judgement to avoid using their superior flying skills.

                          (Again, "watch your speed, especially in an approach in IMC" and "establish a stabilized approach gate" would have worked much better than all that: Superior pilots use their superior judgement to avoid using their superior flying skills.)
                          Thanks for all that. I do, or course agree with what you say, but these are sequential lines of defense we are talking about and not mutually exclusive ones (3WE likes to paint me as someone who dismisses fundamentals because I stress procedure, as if I have to choose between the two). The first, fundamental line of defense is teaching stable approach criteria, sterile cockpit, checklist disipline and attention to airspeed/energy. With that down and religiously adhered to, the chances of getting into an upset are almost nil. That will not always happen however, even to veteran pilots, on a bad day. Fortunately, the second line of defense can still save them if they know it well, so it's important that they do. In this case, I get the impression that there was no stall warning before the upset; the pilot checked the airspeed (after neglecting it, yes) and took corrective action(add power, there was no call for go-around), and that corrective action, being wrong, caused the upset and subsequent, unrecoverable stall. Meaning that if the pilot had taken the appropriate corrective action there would have been no upset and no crash, despite all that sloppy airmanship, and a family would still be alive. Second line of defense. The cornerstone of aviation safety.

                          I think it is fair to say that a pilot with sloppy airmanship can still be expected to execute a recovery correctly. One is a discipline and judgment issue; the other is an instinct and motor skill issue. If a pilot is well-trained, as in your example, to apply right rudder on low-speed, full power application, that pilot may very well be proficient at doing that by having that become an instinctive flying technique, but that same pilot could, on occasion, get sloppy about respecting the rules and monitoring instruments. So we need both lines of defense here, equally well taught.

                          My impression is that issues of the first line of defense are universal, independent of type, whether the aircraft has 98hp or 1500hp, powered flight surfaces or direct cables, etc. This can be taught from the beginning. I already have them down.

                          The second line of defense is not as universal and must be relearned as one transitions to a significantly different aircraft. This seems to be an area that is still neglected. Things like underslung engines and full-length double-slotted flaps can alter the aircraft behavior and thus the procedures.

                          The MU-2 was problematic precisely because it was an affordable, entry-level aircraft into high-power, high-altitude turboprop regime, meaning most pilots transitioning to it had never flown in that regime before. They may have been dead-on with monitoring and following the rules 99.9% of the time, but that one time they got in trouble, their lack or type training only made things worse.

                          Comment


                          • #28
                            They don't really spell out the details of what the pilot tried to do to recover the bank and rapid descent. I would think though if he performed wrong or ineffective measures they would have called it out?
                            I think that the reason why they don't spell out the details THEY DON'T KNOW how the details, since they don't have any source of information for control inputs, control surfaces movement, or angle of attack.

                            --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                            --- Defend what you say with arguments, not by imposing your credentials ---

                            Comment


                            • #29
                              Originally posted by Evan View Post
                              I get the impression that there was no stall warning before the upset.
                              They went as slow as 1 knot above the stall speed. The report says that the stickshaker should have activated, but they could not confirm it because there was nothing to record such data.
                              There is no reason to think that the stickshaker didn't work as designed. Everything seems to be working ok with the plane (except the pilot).

                              --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                              --- Defend what you say with arguments, not by imposing your credentials ---

                              Comment


                              • #30
                                One is a discipline and judgment issue; the other is an instinct and motor skill issue.
                                (not) Monitoring the airspeed in an approach in IMC is not a judgment issue. It's an insctict. A pilot (not an airplane operator) looks at the ASI without even realizing he is doing it.

                                --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                                --- Defend what you say with arguments, not by imposing your credentials ---

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