777 Crash and Fire at SFO

[3WE]

I repeat myself a few times here - for good reason.

Its pretty simple guys. Its called HOLD for a damn good reason. Its HOLDING the thrust.



You've actually answered your own question. Altitude Hold maintains altitude, Heading Hold maintains heading, and Thrust Hold maintains THRUST. There is a SPEED mode, which maintains SPEED on thrust, just as there is a Speed mode of the pitch that maintains speed on elevator. Neither of those are THRUST hold.

The A/T "hold" mode most certainly does do something! It holds the thrust! Yes, sometimes this is after they have reached the IDLE stop, but not always. Its not a speed control mode, its a THRUST control mode. Why would A/T HOLD have anything to do with maintaining speed?!?!?!?!

HOLD is that it HOLDS thrust. That section of the FMA is not the SPEED section. It is the THRUST section.

And sorry Evan, but you are showing a lack of understanding of the system if you think that IDLE HOLD is an appropriate thing for the FMA to say. IDLE is one thing, HOLD is another.

I don't mean to call out this post specifically- but the whole discussion of what this mode should be called...

I'm thinking it should be called OFF

To the best of my recollection, the 172 I learned to fly didn't have autothrottles (it was a 1976 model). And when I pulled the throttle to idle, or firewalled it, or put it somewhere in between it stayed there...of course there was this friction lock thing that was part of the pre-takeoff checklist. (along with setting flaps and slats)...

I'm just not getting why a mode where the autothrottles don't automatically move the throttle's has to have such a fancy cryptic name and acronym.

[MCM]

Because A/T OFF is a different thing. Thats actually when you turn it off.

You need to understand the relationship between autopilot modes to see the difference - if, for example, I select APP mode, if the A/T is turned off, it will stay off. Easy concept - big on/off switch. If the A/T is ON, but is in HOLD, then it is able to change mode to SPD automatically.

I really don't think that HOLD is particularly cryptic or difficult. It just holds the thrust levers where they are.

I've never met any pilots that have had any difficulty using it, or understanding it, in practice. Lets not pretend that is what happened with Asiana. It isn't.

[BoeingBobby]

I don't mean to call out this post specifically- but the whole discussion of what this mode should be called...

I'm thinking it should be called OFF

To the best of my recollection, the 172 I learned to fly didn't have autothrottles (it was a 1976 model). And when I pulled the throttle to idle, or firewalled it, or put it somewhere in between it stayed there...of course there was this friction lock thing that was part of the pre-takeoff checklist. (along with setting flaps and slats)...

I'm just not getting why a mode where the autothrottles don't automatically move the throttle's has to have such a fancy cryptic name and acronym.

Yea, lots of 172's have slats! Type that in blue!

[Gabriel]

I don't mean to call out this post specifically- but the whole discussion of what this mode should be called...

I'm thinking it should be called [I][B]OFF

Except it's not off. It's on, alive and kicking, just deciding not to do anything by now, but closely monitoring the situation and ready to change the previous decision when the conditions are met (for example, as Evan said, if both flight directors had been turned off*)

Maybe STBY would be a good alternate fancy cryptic name and acronym.

* The report mentioned, and Evan highlighted here a few posts ago, that if both flight directors (FD) had been turned off, the AT would have reverted to "Speed hold" mode. I think it's interesting to see why (ok, what I see). And hence the next post.

[Gabriel]

We (I at least) always use the term "autpopilot" loosely. We say "The autopilot is in that mode", "If such condition is met the autopilot does this or that"...

In fact, the autopilot is a dumb executor. It just adjust pitch and bank to comply with the pitch and bank commands it receives. The order comes: "put pitch there". And the autopilot puts pitch there. The autopilot doesn't know if he is doing that to keep a speed, an altitude, a vertical speed or a glide slope. It just blindly follows the order.

And the one giving the order is the flight director. The flight director is the "brains" of the autoflight system. The autopilot is the executing arm. Or better, one of the possible executing arms. The other one being the human pilot. The flight director shows the pitch it wants in the attitude indicator, and there should be some pilot (human or manual) flying the plane and complying with the flight director commands.

The autothrottle doesn't have this "brain-executor" division so clearly marked. It's more "integrated", at least in the eyes of the human pilot: There is no "thrust director" switch. So, unlike the flight director / autopilot combo, the autothrottle switch engages both the brains and the arm of the autothrottle.

And yet, the autothrottle does something with the flight director that the flight director doesn't do with the autopilot: It monitors what the flight director is doing.

I very much disagree with what the NTSB says about the confusing design of the autothrottle and what will it do when the flight director is set to FLCH. I've already said this, but there is only one (okay, two) thing that the pilot needs to understand about this: selecting FLCH is saying "flight director, you have the speed". The second thing is that, because the autothrottle monitors what the flight director is doing, it syas "okay, there must be only one managing the speed at each time, if the master is giving the speed to the flight director, then I will stop managing the speed". So, the ONLY thing that the pilot needs to understand is that selecting FLCH takes speed control away from the autothrottle and gives it to the flight director.

The flight director will then give commands shown in the attitude indicator to adjust the pitch to hold the speed, with the expectancy that some pilot (human or auto) will be complying with those commands and actually adjusting the pitch as instructed. That's why what this pilot did it makes no sense whatsoever: select FLCH (autothrottle, stop holding the speed, flight director, you have the speed), kill the AP (autopilot, don't follow the flight director commands, i.e. don't hold the speed) and not follow the flight directors command himself (I will not hod the speed either). So who is managing the speed now? Newton.

Returning to the autothrottle, when FLCH is selected it stops holding the speed but keeps monitoring the flight director to be sure that it is in a mode where it will give commands to hold the speed. (Note, however that the autothrottle will not verify if there is someone, human or auto, effectively complying with said flight director commands). If the flight director stops being in a mode where it is supposed to control the speed, the autothrottle will say "ok, the flight director is not controlling the speed anymore, I am on, so I'll take the speed again". That happens when the plane is climbing and descending in FLCH mode and the plane reaches the selected altitude: the flight director reverts to "altitude hold", so it's not in FLCH anymore, the autothrottle detects that, and reverts to speed hold mode.

And, finally, another case would be switching the flight director off. If that happens, the autothrottle will say "the flight director is not controlling the speed anymore, I am on, I will take the speed". But that takes to switch both flight directors off, because as long as one of them is on and in a mode that controls speed, it will assume that some pilot, human or auto, is following the FD commands and hence controlling the speed.

And in this case, there was a very good reason for the pilot to switch the flight directors off: he had no intention to follow its commands.

So:
- he selects FLCH and gives speed control to the flight director (the brain), but kills the AP (the executing arm of the flight director).
- he manually flies with no intention to follow the flight director commands, but he leaves the flight director on.

I disagree with MCM. I really don't think that he understood the modes involved. Either that, or he made his best effort to deceive the system.

[MCM]

We'll have to disagree then Gabriel.

My strong belief is that the crew involved would be able to recite to you exactly what those modes did. But, on the day, in the heat of battle, did not work as a team, set modes without the other knowing, and when it all got too hard, correctly disconnected the A/P, but kept the A/T in, unaware they were in an inappropriate A/T mode. Thats also the reason they didn't fly with the FD off - when you've done hundreds of approaches with it turned on, it isn't instinct, in the heat of battle, to turn it off.

[Gabriel]

We'll have to disagree then Gabriel.

My strong belief is that the crew involved would be able to recite to you exactly what those modes did.

Sure, but one thing is to recite the manuals and another is to understand, and not just the what, but also the how and why.

But, on the day, in the heat of battle, did not work as a team, set modes without the other knowing, and when it all got too hard, correctly disconnected the A/P, but kept the A/T in, unaware they were in an inappropriate A/T mode. That's also the reason they didn't fly with the FD off - when you've done hundreds of approaches with it turned on, it isn't instinct, in the heat of battle, to turn it off.

Well, maybe.
I'm sure that they didn't work well as a team.

But if I didn't misunderstood the sequence, I have the impression that the person selecting FLCH, the person turning the AP off, the person flying manually, the person not following the FD commands, the person not turning the FD off, the person who moved the throttles to idle, the person who didn't advance them, the person who said that he expected that the autothrust would hold the speed, and the person who said that he was afraid or visual straight-in approaches with long finals with no obstacles to long runways with PAPI on beautiful days, were all the same person: the pilot flying. So it's not like if someone else had selected FLCH, turned the AP off or iddled the throttles without him knowing.

He also failed to express what he was doing, and the other two guys failed to monitor the flight parameters, the flight path trajectory, the stabilized approach (which includes not having the thrust at idle) and calling a go around in time. So yes, they failed as a team too.

[Evan]

We'll have to disagree then Gabriel.

My strong belief is that the crew involved would be able to recite to you exactly what those modes did.

Maybe they could recite what they do when they are used appropriately, or even inappropriately with ILS available, but I doubt they would recite the pitfalls of this given set of circumstances.

[Gabriel]

Final report out. I haven read it yet.

http://www.ntsb.gov/doclib/reports/2014/AAR1401.pdf

[elaw]

I have. There's nothing too surprising in there - discussion of bad airmanship, not enough focus on hand-flying (especially approaches), and automation mode confusion. Probable cause is as you'd expect: they got too low & slow while trying to recover from being too high and fast, weren't able to arrest the descent, and hit a seawall. Contributing was misunderstanding of how the a/t worked, and possibly fatigue. They do give a nod to the 777's crashworthiness, noting the number of survivors in spite of the severity of the crash.

There is one thing I did find interesting. In the main report, and even more so in some of the members' statements afterward, they seem to imply that because the pilots thought the a/t would correct for too-low airspeed under all conditions, that maybe the a/t's functionality should be modified to do just that.

But to me that seems very impractical for one reason. Suppose that at the very bottom of descent when the pilot pulled back on the yoke, instead of there being a seawall in front of the main wheels, there was a runway a few feet beneath them. In that case what they were doing would not be called "crashing", it would be called "flaring". How would the a/t know the difference between the two? If during the flare it suddenly decided airspeed was too low and firewalled the throttles, that wouldn't work out too well, would it?

[Gabriel]

I agree with you. I have commented on this several times during this thread: why the speed protection is disabled when the throttles are manually idled and the altitude in below 100ft RA. The plane thinks that you are flaring and adding thrust would not be a good move.

[Evan]

They had glidepath guidance on the ND.

The FMC computes a performance - optimized descent path , assuming idle thrust from the top of descent, that meets all airspeed and altitude constraints and the end of descent point in the flight plan. During descent, once the top of descent has been passed, a vertical path indicator (VPI), consisting of a path pointer and deviation scale, is displayed on t he lower right side of the ND (see figure 7). The VPI shows the airplane’s vertical distance above or be low the computed descent path. If the FMC has been programmed for a LOC procedure, the airplane’s vertical navigation (VNAV) system computes a vertical path from the FAF to the runway threshold. From the FAF to the runway, the VPI shows the airplane's vertical distance above or below the computed glide path for the approach regardless of whether or not the ILS glideslope is functional.

They had correct information on FLCH/AT interaction (if they could read the FCOM):

The A/T automatic engagement feature was described in the Asiana 777 FCOM, chapter 4, “Automatic Flight,” page 4.20.9, as follows:

The autothrottle can support stall protection when armed and not activated. If speed decreases to near stick shaker activation, the autothrottle automatically activates in the appropriate mode (SPD or THR REF) and advances thrust to maintain minimum maneuvering speed (approximately the top of the amber band) or the speed set in the mode control speed window, whichever is greater. The EICAS message AIRSPEED LOW displays. Note: When the pitch mode is FLCH or TOGA, or the airplane is below 400 feet above the airport on takeoff, or below 100 feet radio altitude on approach, the autothrottle will not automatically activate.

Then there's culture...

In a postaccident interview, the PF stated that at 500 ft AFE, the airplane should be stabilized, and for a visual approach , the airplane should be stabilized by 300 ft AFE . For an unstable condition, he said a go - around should be performed . The PF stated that only the PIC, in this case the PM, had the authority to decide to go around. He said this was company policy resulting from a tailstrike event that had occurred when an FO had initiated a go around.

Annnnd more culture...

The [Asiana scripted] “Automatic Flight System” transition training module and the “B777 Flight Controls – Recurrent Training” module did not indicate that the low speed protection function provided by the A/T would not activate if the A/T was in HOLD mode. In a written statement, an Asiana 777 ground school instructor indicated that although the information was not included on any slides, he explained during a 777 ground school class attended by the PF that the A/T would sometimes remain in HOLD mode after the A/P was disconnected and airspeed could drop. He described this as an “anomaly in the Boeing 777’s auto throttle functioning” that he had personally experienced on three separate occasions. He said he advised students that this could occur during a high energy descent in FLCH mode and that if they encountered this situation, they should change the AFDS pitch mode to V/S or VNAV. An Asiana pilot who was in this instructor’s class with the PF reviewed his class notes and confirmed that the instructor had provided this information. The same student stated that another instructor had provided similar information during another 777 ground school class attended by the PF and advised students that they should not use FLCH to descend after crossing the FAF.

And the resulting technical ingnorance...

The PF stated that the 777 A/T system would always maintain the selected airspeed as long as the A/T was on. He said that if a pilot overrode the thrust lever s manually, the A/T would resume controlling airspeed when the pilot released the thrust levers. He stated that it was irrelevant whether he had pushed the FLCH button immediately before disconnecting the A/P during the accident approach because he was in manual flight and the A/T was always working. He thought the A/T should have automatically advanced the thrust levers upon reaching the MCP - selected airspeed during the accident approach, and he did not understand why that did not occur. Furthermore, he thought the A/T system should have automatically transitioned to TO/GA when the airplane reached minimum airspeed. In that respect, he believed that the 777 A/T functionality was similar to alpha floor protection on the Airbus A320/321. 88 Asked how confident he was in his understanding of the 777 AFCS , he said he had followed the Asiana training program but was not confident in his understanding, and he thought he needed to study more.

And finally, in case you might think this is just an Asiana problem, there's this gem:

Industry statistics indicate about 97% of unstable approaches are continued to landing (Burin 2011)

[Evan]

I was wrong about one of my earlier assumptions concerning the abuse of FLCH in this case. Instead of using an MCP altitude that is too low and unsafe (such as 0') to achieve and maintain idle thrust and a rapid altitude change, this pilot had left in an MCP altitude that was too high (3000', well above their present altitude). This resulted in the A/P commanding pitch up, which prompted the confused pilot to disengage the A/P. The MCP reference speed was also too high, prompting the A/T to increase thrust (as it was in THR mode), which in turn prompted the pilot to manually retard the thrust levers and thereby change the A/T mode to HOLD. This is further evidence of his inadequate training on the AFCS. Because FLCH SPD is designed to achieve a selected flight level, entering that altitude is part of the modal sequence. Obviously he didn't think to notice that altitude shown on the MCP when he chose FLCH, choosing it purely for the A/T effect he was expecting (IDLE).

It's frightening to think that crews can be type-rated without such basic understanding of automation or basic monitoring discipline.

But to me that seems very impractical for one reason.

It's impractical for another reason as well:

This problem might be ameliorated by eliminating the inconsistency of the A/T’s behavior when the pilot’s manual throttle override occurs in different pitch modes. However, the HOLD mode is so thoroughly integrated into the 777 AFCS that removing this inconsistency might be impractical because it would require a fundamental redesign of the 777 and 787 AFCS.

[ATLcrew]

It's frightening to think that crews can be type-rated without such basic understanding of automation or basic monitoring discipline.

There are people who are type-rated and who can barely fly, automation or otherwise. And not just in Korea either, I'm afraid.

[Gabriel]

Annnnd more culture...

And the resulting technical ingnorance...

I think that there are two big, gross, immense conceptual issues that are being grossly, immensely overlooked even by the NTSB:

1- When you select FLCH you are instructing the AT to STOP HOLDING THE SPEED by controlling the thrust, and at the same time, instruct the FD to give command-bars indications to hold the speed by controlling the pitch. IF the AP is engaged, then the AP will obey the FD indications and hold the speed for you by controlling the pitch. If the AP is off, they YOU have to follow the indications of the FD to hold the speed. If you instructed the AT to stop holding the speed, instructed the FD to give pitch command indications to hold the speed, instructed the AT not to follow those pitch commands (by disengaging it), and you don't manually adjust either the thrust (then why did you select FLCH) or the pitch (following the FD command bars) to control the speed yourself, then NO ONE is controlling the speed.
Pilots, take note: in FLCH (and similar "pitch controls speed" modes) the AT IS NOT SUPPOSED TO, AND DOESN'T, CONTROL THE SPEED. (this little dot is a PERIOD). So don't count with it to do it. I propose to re-brand this mode: "PNTCS": "Pitch, Not Throttles, Controls Speed". Maybe that will make it more clear.

2- The speed protection is a speed PROTECTION. It's a safety belt. An airbag. A lifesaver. NOT A TOOL for the pilot. Even if the AT system would have been designed to prevent a stall in this situation (what it wasn't because the situation looks like a flare) AND if the pilot was not supposed to monitor the flight parameters that are being controlled by the automation (to take corrective action in case it's not performing as expected), even the YOU MUST NOT RELAY ON A PROTECTION ON AN OPERATIVE BASIS.
Q: What is the GPWS warning that says "Too low. Gear!"?
A: It is the indication that you have to lower the gear.
NOT!!!!!
It is the indication that you, idiot, forgot to lower the gear yourself and then failed to detect that condition in the landing checklist. If it sounds, you have already screwed up big time!!!!
There is even a name for this "human factor" and all: Primary-backup inversion (when what is supposed to be a backup, safety feature is taken as a primary, operative tool).

Why does the NTSB fail to mention those two "little" CRUCIAL details?

Why does the NTSB, instead, discuss at length about how, in certain cases, regardless that the pilot had told it not to do so, the AT will kick in and says "okay... okay... we are too slow so it seems that John Pitch is not controlling the speed as it should, so better I handle it myself and save the day". And that, since in some cases it will do that and in others it won't, then how that could confuse the pilots WHO SHOULD NEITHER CARE, NOR TAKE INTO ACCOUNT, NOR RELY on this PROTECTION LIFE SAVING function for their operative decisions and actions to begin with. It's like saying "The pilot didn't lower the gear because he expected the GPWS to sound the "too low, gear" warning and, in this particular scenario it will not. It's confusing for the pilots that in some circumstances it will alert them and in others not, and that confusion might make that a pilot to forget to lower the gear because he could be waiting for a gear warning that would not come". NOT!!! This condition can make that a pilot that ALREADY FORGOT to lower the gear AND FAILED TO DETECT IT in the landing checklist lends with the gear up, but IT CAN NOT CAUSE a pilot to forget to lower the gear (as long as the pilot is not relying in this alarm to tell him when to lower the gear, but don't blame the GPWS in that case!!!)

Is this really so hard to understand?