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Were new procedures in Dubai airspace a factor in Emirates crash?: FlightAware

Discussion in 'Airport News, Talk & Discussion' started by Lord Leighton, Aug 12, 2016.

  1. Lord Leighton

    Lord Leighton Hangar Gold Member I

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    Low Missed Approach Altitude Restrictions

    A question concerning a recent change to the missed approach procedures in Dubai UAE (OMDB) has raised some interesting points about the 777 in this flight regime: high thrust, low altitude, high pilot workload, and ATC procedures that would seem to be not too well thought out.

    Specifically the new procedure introduces a not-above altitude of 1300 ft AMSL after going around from a near sea level Precision or GPS approach minimum (1000 ft missed approach climb).

    As any pilot of a two engine jet aircraft can tell you that an early level off in the missed approach is not a good thing. Typically, anything below 3000 ft introduces a significant workload on the pilots – and that’s when the missed approach is straight ahead, the autopilot is engaged and the aircraft fully functional. Add some manual flight and a non-normal element to this… the Sandpit pilots must be just loving this new procedure in the simulators in Dubai. The French did an extensive study [​IMG] on errors made during the missed approach and the folly of low altitude requirements in the missed approach path was just one of their conclusions.

    [​IMG]
    This new procedure initially tracks straight ahead from the Missed Approach Point (MAP) (that’s a good thing) to DB710 – but requires the crew to level off at 1300 ft AMSL (Not so good). It then requires level flight for approximately 3nm (why? why?) during which a turn must be commenced (at DB710), and then finally the missed approach climb segment may be continued (from DB711) to the final Missed Approach Altitude (MAA) of 3000 ft AMSL.

    [​IMG]
    Multiple altitude requirements in missed approaches are nothing new. Typically, however, they are must-reach-by or at-or-above requirements to ensure terrain clearance, rather than “Stop” altitudes like this one. I haven’t looked around for a while, but I can’t actually recall a missed approach quite like this one.

    That’s why I jumped into the simulator today and ran through it just to see what it looks like. Looking at the chart it looks like a dog’s breakfast; looking at it in the simulator I was not disappointed.

    There clearly must be a reason driving this procedure. For the life of me I can’t think of an obstacle related one, unless a Sheikh has placed a permanent hot air balloon at 2000 ft off the end of the runway to see the sights, one of which is watching aircraft sailing by under his balloon at 1300 ft. Remember, this is Dubai… it could happen.

    I can only assume that this altitude requirement in some way keeps aircraft going round from tangling with aircraft either (a) going around; or (b) approaching in the opposite direction on the other runway. In either case it’s a poor excuse for the potential cluster this introduces into the flight deck.

    Thrust, Lots of Thrust
    The biggest problem with these early level offs is Thrust. The 777 Autothrottle is supposed to limit thrust on a two engine go-around from full thrust back to a setting that guarantees at least 2000 fpm. It does this very, very well. In fact, it does this so well that you usually get well over 3500+ fpm by the time things have settled down, which by definition is at least 2000 fpm, but it’s not particularly helpful when you’re trying to keep control of your aircraft. You have to remember these engines are designed to lift 350 Tons of aircraft (with one engine failed). Lifting the aircraft’s 250 ton landing weight on both engines is an underwhelming task to say the least. All two engine aircraft are fundamentally overpowered right up until the point where one of the engines fail.

    Additionally, the link between the software of the Autothrottle and the software of the AFDS Takeoff Go-Around (TO/GA) and Altitude Capture (ALT) modes is a tenuous one – in fact there isn’t one really. As such each and every time I ran this scenario – unless the pilot intervened – the 1300 ft restriction was exceeded by at least 100 ft because there was simply too much thrust/energy for the autopilot to capture the altitude adequately. This probably won’t set off alarm bells in the ATC center or the airline Flight Data Monitoring (FDM) programs. But it doesn’t look good in the sim on your check.

    The really cool thing is that after this minor bust you’re about 1300 feet above the ground shortly after a go around and sinking back down to your required altitude – you guessed it, several times the GPWS [​IMG] activated to give me a stern “DON’T SINK” caution. It’s a good thing really. Because I spend far too much time operating this aircraft safely within the best practice envelope, I just don’t get enough practice at listening to GPWS warnings. It’s nice to know I can go somewhere in the world and operate the aircraft as the manufacturer intended but still get to hear “DON’T SINK” after the go-around.

    What to do?
    Well, you have a couple of options, all based around manual flight intervention. You could disconnect the AP early in the maneuver and manually capture the altitude, avoiding the altitude bust. Nothing is for free however, your workload will increase significantly also increasing the likelihood of error. Meanwhile, your thrust won’t be behaving any differently, so as you push forward manually on the flight controls to capture your altitude (giving your passengers a free roller-coaster feeling) you’re likely to get an small overspeed as the thrust levers struggle to catch up. Options to fix that include overriding the Autothrottle temporarily and reducing thrust to contain the speed/altitude, or going full manual on the thrust. You thought the workload was higher going manual early in the missed approach? How is it now? The truth is that there just isn’t a simple, appropriate fix to this problem. If there was, the Autopilot would have been able to do it.

    When to Accelerate
    With an intermediate level off prior to the final MAA, the question occurs – when will you accelerate and retract Flap? Initially, the speed will be flown based on the approach speed, with one stage of flap retracted in the go-around maneuver. You will typically be operating at Flap 20 and you’re a few knots below Flap 20 minimum speed, which is considered acceptable when you have a massive amount of thrust on and you’re rocketing up for the sky. But since you have not reached the final MAA, most airlines will require their pilots to retain this slower speed to ensure terrain clearance in the subsequent sectors of the missed approach procedure until reaching MAA or an earlier altitude that guarantees terrain clearance. As discussed elsewhere, typically terrain clearance for intermediate acceleration in the missed approach is not assessed – and there’s no indication that it has been assessed here. The presence of a 768 ft obstacle just at DB711 where you’re still held down at 1300 ft for no obvious reason isn’t encouraging. So the chances are you’ll want to retain your initial missed approach speed until you finally reach the MAA of 3000 ft AMSL.

    [​IMG]
    But as your Autopilot Flight Director System (AFDS) captures 1300 feet as set in the Mode Control Panel (MCP) Altitude Selector – the speed automatically jumps up and the aircraft accelerates away, taking the decision away from the unaware pilot. Thrust – which is already very high for a 1000 ft altitude change – now increases as it’s released from the shackles of only needing to provide at least 2000 fpm, and instead drives to full GA thrust in order to accelerate the the Flap limit speed. Given this occurs as you’re still trying to level at 1300 ft – you can see why the altitude bust keeps occurring.

    [​IMG]
    Dubai NOTAM

    It’s worth noting that any physical change in the MCP Selected Speed after the TO/GA mode has been activated disarms the speed jump up when ALT captures. I demonstrated this several time today. Once established safely in the go-around (Flight Mode Annunciator (FMA) modes verified; positive climb; Gear Up) – when the “Four Hundred” foot call was made I reached up and increased the selected speed by one knot. With this done, the speed remains at go-around speed when the AFDS ALT captures. This technique works even if you change the speed and then reset it to the initial go-around speed; or simply set it to the minimum speed for your go-around flap setting (Flap 20 or Flap 5) for a more comfortable level segment at 1300 ft.

    In any case, since most international airlines do not accelerate in the missed approach until reaching either MAA or a point at which terrain clearance is assured, you will NOT want to let the aircraft accelerate. This means winding the speed back after ALT capture. The later you managed to do this, the longer you’ll be under large thrust settings.

    Missed Approach Commenced Above MAA
    In my Procedures and Techniques document, I have a small paragraph on commencing the Missed Approach from above MAA and a suggested technique for it. We experience this occasionally in KLAX where the approaches often commence from 4000 ft – but the MAA is 2000 ft.

    When commencing a missed approach like this one where you’re actually higher than an altitude requirement – the standard procedure of TO/GA, pitch/thrust, gear won’t help – you actually want to continue the descent down the approach to the altitude restriction (1300 ft). For a precision approach the priority is to deselect Approach (APP) mode. By design an engaged APP mode will fly you straight through your 1300 ft requirement.

    Additionally if you’re in APP mode at 1500 ft it locks in and you’re only way out of LOC/GS at that point is to disconnect the Autopilot AND cycle both Flight Directors OFF. Having deselected APP the AFDS should be in HDG/TRK and VS. Laterally, LNAV is probably the best choice (is your active waypoint ahead of you?), and VS will suit you fine until you capture either MAA or the lower requirement (in this case the 1300 ft). If you’re capturing MAA (such as in KLAX) you now have the option of accelerating and cleaning up. But for this strange procedure – you may need to maintain your approach speed flying level until you eventually reach the final MAA of 3000 ft. Don’t forget to raise the gear at some point!

    In Summary
    Odd procedures like this expose some of the limitations of our aircraft, it’s systems and our procedures. It’s worth running a few of these low altitude captures next time you’re in the simulator.

    Finally, a recent NOTAM indicates that UAE ATC may have had a change of perspective on this procedure. Whether this comes from operational experience and results in a permanent change – we’ll have to wait until the next documentation cycle to find out.​
     
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  2. Lord Leighton

    Lord Leighton Hangar Gold Member I

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    Interesting to say the least! :eek:o_O
     
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  3. xnwa

    xnwa Hangar Bronze Member III

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    I read somewhere {forgot where} that the 777 that crashed in Dubai was given clearance to land by ATC a short time later was told climb to 4000 ft. .........Missed approach?
     
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  4. Lord Leighton

    Lord Leighton Hangar Gold Member I

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    Probably read it in my post on the report of the crash shortly after it happened? Maybe ATC hadn't yet read the new procedures themselves? :confused::eek:
     
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  5. Flytdeck

    Flytdeck Hangar Bronze Member VI

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    Great article. The missed approach from ABOVE the MAA is an event that rarely happens and is NEVER practiced in the simulator. My technique is to select go-around then select altitude hold so that the power does not go crazy. Then select either Flight Level Change or Vertical speed to descend to the altitude. Selecting go-around threads the navigation into the proper sequence so LNAV stays active. Once everything is stable and checked, then the speed can be selected to accelerate and the flaps retracted on schedule. This sequence slows everything to a manageable speed in an unusual environment (I LIKE slow).

    A senior Emirates pilot (now retired) was commenting on the hazards of a touch and go-around when it comes to thrust management. Still waiting for the initial report.
     
  6. Flytdeck

    Flytdeck Hangar Bronze Member VI

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    This is the article referenced in my previous post:

    Emirates B777 crash was accident waiting to happen
    BYRON BAILEYThe Australian12:00AM August 9, 2016

    The crash of an Emirates B777 during an attempted go-around in Dubai last Wednesday was always an accident waiting to happen.

    It was not the fault of the pilots, the airline or Boeing, because this accident could have happened to any pilot in any airline flying any modern glass cockpit airliner — Airbus, Boeing or Bombardier — or a large corporate jet with autothrottle.

    It is the result of the imperfect interaction of the pilots with supposedly failsafe automatics, which pilots are rigorously trained to trust, which in this case failed them.

    First, let us be clear about the effect of hot weather on the day. All twin-engine jet aircraft are certified at maximum takeoff weight to climb away on one engine after engine failure on takeoff at the maximum flight envelope operating temperature — 50 degrees C in the case of a B777 — to reach a regulatory climb gradient minimum of 2.4 per cent.

    The Emirates B777-300 was operating on two engines and at a lower landing weight, so climb performance should not have been a problem. I have operated for years out of Dubai in summer, where the temperature is often in the high 40s, in both widebody Airbus and Boeing B777 aircraft.

    Secondly, a pilot colleague observed exactly what happened as he was there, waiting in his aircraft to cross runway 12L. The B777 bounced and began a go-around. The aircraft reached about 150 feet (45 metres) with its landing gear retracting, then began to sink to the runway.

    This suggests that the pilots had initiated a go-around as they had been trained to do and had practised hundreds of times in simulators, but the engines failed to respond in time to the pilot-commanded thrust. Why?

    Bounces are not uncommon. They happen to all pilots occasionally. What was different with the Emirates B777 bounce was that the pilot elected to go around. This should not have been a problem as pilots are trained to apply power, pitch up (raise the nose) and climb away. However pilots are not really trained for go-arounds after a bounce; we practise go-arounds from a low approach attitude.

    Modern jets have autothrottles as part of the autoflight system. They have small TOGA (take off/go-around) switches on the throttle levers they click to command autothrottles to control the engines, to deliver the required thrust. Pilots do not physically push up the levers by themselves but trust the autothrottles to do that, although it is common to rest your hand on the top of the levers. So, on a go-around, all the pilot does is click the TOGA switches, pull back on the control column to raise the nose and — when the other pilot, after observing positive climb, announces it — calls “gear up” and away we go!

    But in the Dubai case, because the wheels had touched the runway, the landing gear sensors told the autoflight system computers that the aircraft was landed. So when the pilot clicked TOGA, the computers — without him initially realising it — inhibited TOGA as part of their design protocols and refused to spool up the engines as the pilot commanded.

    Imagine the situation. One pilot, exactly as he has been trained, clicks TOGA and concentrates momentarily on his pilot’s flying display (PFD) to raise the nose of the aircraft to the required go-around attitude — not realising his command for TOGA thrust has been ignored. The other pilot is concentrating on his PFD altimeter to confirm that the aircraft is climbing due to the aircraft momentum. Both suddenly realise the engines are still at idle, as they had been since the autothrottles retarded them at approximately 30 feet during the landing flare. There is a shock of realisation and frantic manual pushing of levers to override the autothrottle pressure.

    But too late. The big engines take seconds to deliver the required thrust before and before that is achieved the aircraft sinks to the runway.

    It could have happened to any pilot caught out by an unusual, time-critical event, for which rigorous simulator training had not prepared him.

    Automation problems leading to pilot confusion are not uncommon; but the designers of the autoflight system protocols should have anticipated this one. Perhaps an audible warning like “manual override required” to alert the pilots immediately of the “automation disconnect”.

    My feeling is the pilots were deceived initially by the autothrottle refusal to spool up the engines, due to the landing inhibits, and a very high standard of simulator training by which pilots are almost brainwashed to totally rely on the automatics as the correct thing.

    Byron Bailey is a commercial pilot with more than 45 years’ experience and 26,000 flying hours, and a former RAAF fighter pilot. He was a senior captain with Emirates for 15 years.
     
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  7. Lord Leighton

    Lord Leighton Hangar Gold Member I

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    Now that makes sense!
     
  8. Flytdeck

    Flytdeck Hangar Bronze Member VI

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    It is worse than that. Pilots are becoming AFRAID to disconnect automatics and manually control the aircraft. Some airlines PROHIBIT disconnecting the autothrust system altogether therefore there is no instinctive effort to manipulate the thrust levers as required, a motor skill embedded in most pre-glass cockpit pilots. This brings about a direct conflict with aircraft design, training, daily operations, and basic flying skills.
     
  9. Lord Leighton

    Lord Leighton Hangar Gold Member I

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    Don't forget the stupid 'honor' culture extended to the cockpit. Perfect example of all these things considered: Asiana 214 at SFO on a perfect day/conditions for flyin WITH 4 crew in the cockpit..
     
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  10. Flytdeck

    Flytdeck Hangar Bronze Member VI

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    The "flight deck gradient" and a BIG problem in Asian, Russian, and Indian carriers. A problem in Latin America but not so much in the rest of the world and it is eroding. Even Japanese carriers are making strides to eliminate this cultural aviation barriers, and their gradient was one of the steepest 35 years ago. Sadly, it it is one of the many indications that the human element is the most fallible component in the system.
     
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  11. Jay Meinen

    Jay Meinen New Hangar Member

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    My Jepps dated10 June 16 don't show a max altitude on missed approach. Is this a change from the chart depicted, 24 March 16?

    I know that a missed approach can be a very busy time. Throw in one more threat (max altitude) and I can certainly see how something unexpected can happen.
     
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