CaptainLars

Trying to follow TCAS instructions...

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Hi,

the following happened to me when climbing out of Sheremetyevo 06L using the 777 freighter:

At approximately 2000ft, I got a traffic warning (in yellow). I looked out of the window and couldn't see anything. A few seconds later, I got the red traffic alert, the system telling me to descent, which I did, of course. Then "increase descent". At the end I descended with up to 5500ft/min and picked up a lot of speed, 335kts. Of couse, since the alarm silenced, I wanted to climb again, and that worked... 5500ft/min climb, the speed slowly coming down to 250kts again.

However, I didn't want to climb that fast, instead I would have preferred to do a more gentle climb, reducing power perhaps. But this was impossible. I pressed the yoke hard down, all the way, but the plane did not react, only to lateral input. I also wanted to reduce power, since we were so awefully fast, and I feared for the structural integrity of the plane (I think I even used speedbrakes in one moment), but this was impossible, too, and it wasn't possible to disconnect the Autothrottle.

So I guess that I met the Flight Envelop Protection. Is it correct that the plane behaves that way? I would have expected such behaviour in an Airbus, not in a Boeing. Would it have been possible to take *more* control of the aircraft by deactivating Flight Director and switching A/T totally off? A/P wasn't on after all.

I'd appreciate any input on this situation... tbh, it was a bit scary! :ohmy:

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When you changed from climb to descent you didn't describe the actions you took.  Did you cancel autopilot?  What about thrust mode?  How do you disconnect A/T?  Never necessary to deactivate FD.... it is not flying only guiding.

Give a scenario where I was climbing through 2000 feet, probably clean with N1 thrust and speed pitch (VNAV SPD) and had to descend, I would disconnect A/T and A/P then pull power off then nose down and keep the speed under control using speedbrakes if necessary until clear of alarm.  First rule of flying is fly the airplane first.

I have controller buttons programmed to disconnect A/P and A/T. 

I don't like AI traffic, very unrealistic, and never had this happen but I bet it woke you up.

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As a general point: a TCAS RA should never be a violent manoeuvre and it would be unusual that such a high rate of descent would be necessary. All that is necessary is to keep the VSI in the green region and/or pitch smoothly to avoid the red region on the PFD. -5500 fpm at 2000ft is not a place I would like to be!

Step 1 on receiving a TCAS RA is to disconnect both autopilot and autothrottle (FDs can stay on but must not be followed in pitch until clear of conflict). Can you normally disconnect the A/T in flight?

I'm afraid I don't know enough about the B777 flight control/protection systems to answer the rest of your question, sorry! 

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14 hours ago, CaptainLars said:

Hi,

the following happened to me when climbing out of Sheremetyevo 06L using the 777 freighter:

At approximately 2000ft, I got a traffic warning (in yellow). I looked out of the window and couldn't see anything. A few seconds later, I got the red traffic alert, the system telling me to descent, which I did, of course. Then "increase descent". At the end I descended with up to 5500ft/min and picked up a lot of speed, 335kts. Of couse, since the alarm silenced, I wanted to climb again, and that worked... 5500ft/min climb, the speed slowly coming down to 250kts again.

However, I didn't want to climb that fast, instead I would have preferred to do a more gentle climb, reducing power perhaps. But this was impossible. I pressed the yoke hard down, all the way, but the plane did not react, only to lateral input. I also wanted to reduce power, since we were so awefully fast, and I feared for the structural integrity of the plane (I think I even used speedbrakes in one moment), but this was impossible, too, and it wasn't possible to disconnect the Autothrottle.

So I guess that I met the Flight Envelop Protection. Is it correct that the plane behaves that way? I would have expected such behaviour in an Airbus, not in a Boeing. Would it have been possible to take *more* control of the aircraft by deactivating Flight Director and switching A/T totally off? A/P wasn't on after all.

I'd appreciate any input on this situation... tbh, it was a bit scary! :ohmy:

TCAS RA memory item is 

AP off and A/THR off

if you only disconnect A/P during initial climb out, your Thrust setting would still be in CLB thrust at that stage. 

Therefore with the pitch down command and the thrust at CLB thrust setting, your speed and rate of descend will run away very quickly. 

Once the TCAS is gone, your airplane had already carried a lot of overspeed from the previous nose down maneuver, if you raise you nose to back to you original climb out attitude ~8-9deg, you will get 5000+ ft rate of climb and it is normal. 

 

If you follow the TCAS memory item (which is manual thrust + manual flying) it would prevent you from getting into the scenario you experienced. 

 

Airbus TCAS RA memory item is autopilot off and FD off. This way the A/THR will be in SPD model, therefore would try to maintain the target airspeed of the airplane regardless of pitch command. 

 

When i I first came to the 777 from the airbus, I had once questioned why the 777 could not fly the TCAS RA maneuver in the Airbus way i.e switch off the FD only and force the A/THR mode into SPD mode.

Obviously the answer was Boeing needs to align TCAS RA memory items across all the Boeing aircrafts including the older 744 and 767 which used to have a policy of "manual flying must couple with manual thrust" 

 

 

 

 

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18 hours ago, downscc said:

When you changed from climb to descent you didn't describe the actions you took.  Did you cancel autopilot?  What about thrust mode?  How do you disconnect A/T?  Never necessary to deactivate FD.... it is not flying only guiding.

Give a scenario where I was climbing through 2000 feet, probably clean with N1 thrust and speed pitch (VNAV SPD) and had to descend, I would disconnect A/T and A/P then pull power off then nose down and keep the speed under control using speedbrakes if necessary until clear of alarm.  First rule of flying is fly the airplane first.

I have controller buttons programmed to disconnect A/P and A/T. 

I don't like AI traffic, very unrealistic, and never had this happen but I bet it woke you up.

I didn't have A/P engaged, so I immidiately followed the TCAS instructions. At first I didn't switch off A/T, only later. I have a button of my hardware throttle unit mapped to the A/T disengage button on the simulator throttles that I usually use for disconnecting A/T upon approach.

 

17 hours ago, skelsey said:

As a general point: a TCAS RA should never be a violent manoeuvre and it would be unusual that such a high rate of descent would be necessary. All that is necessary is to keep the VSI in the green region and/or pitch smoothly to avoid the red region on the PFD. -5500 fpm at 2000ft is not a place I would like to be!

Step 1 on receiving a TCAS RA is to disconnect both autopilot and autothrottle (FDs can stay on but must not be followed in pitch until clear of conflict). Can you normally disconnect the A/T in flight?

I'm afraid I don't know enough about the B777 flight control/protection systems to answer the rest of your question, sorry! 

Yes, at 2000ft I was still climbing. It was a curve that led me back to 2000ft at the end of the manoeuvre.

 

6 hours ago, Driverab330 said:

TCAS RA memory item is 

AP off and A/THR off

if you only disconnect A/P during initial climb out, your Thrust setting would still be in CLB thrust at that stage. 

Therefore with the pitch down command and the thrust at CLB thrust setting, your speed and rate of descend will run away very quickly. 

Once the TCAS is gone, your airplane had already carried a lot of overspeed from the previous nose down maneuver, if you raise you nose to back to you original climb out attitude ~8-9deg, you will get 5000+ ft rate of climb and it is normal. 

 

If you follow the TCAS memory item (which is manual thrust + manual flying) it would prevent you from getting into the scenario you experienced. 

 

Airbus TCAS RA memory item is autopilot off and FD off. This way the A/THR will be in SPD model, therefore would try to maintain the target airspeed of the airplane regardless of pitch command. 

 

When i I first came to the 777 from the airbus, I had once questioned why the 777 could not fly the TCAS RA maneuver in the Airbus way i.e switch off the FD only and force the A/THR mode into SPD mode.

Obviously the answer was Boeing needs to align TCAS RA memory items across all the Boeing aircrafts including the older 744 and 767 which used to have a policy of "manual flying must couple with manual thrust" 

Thank you very much for your detailed insight, and for confirming what Dan and Simon said.

 

What I see from your answers is that my "mistake" was not to disengage A/T right away and not using speedbrakes enough. Of course, the biggest fault was just trusting the ATC takeoff clearance when the aircraft on the parallel runway had just received T/O clearance, too.

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Right. 

Put it this way, the Boeing Memory items says very clearly the TCAS RA action is AP of + A/T off.

 

so I guess you were right, it would be your "mistake" for not disconnecting the A/T immediately after disconnecting the AP. 

 

But it unlike the real airplane where the A/T disconnect switch is placed at a very convenient location for quick disconnect of the A/T. There will inevitably delays in Flight sim. And this is not your fault unless you have a Boeiny style throttle quadrant. 

 

Just like I have mentioned above if you have a climbing attitude of 8-9deg with 85% N1 (usual CLB thrust settings), and you get a Descend RA command, the pitch change will be quite dramatic and any delay to pull back the thrust will lead to an overspeed. 

 

I didnt mentioned anyway about overspeed recovery in my post. So I did not comment on your use of speedbrake. 

 

If you try to replicate the same scenario again and the TCAS RA, see if you can effectively control the speed by taking out the A/T asap. 

There was an event similar to what you had encountered actually had happened to one of our company 777 takin off from SFO a few years back. 

They were climbing out from 28L and there was a VFR traffic crossing their flight path at ~3000ft which generated a descend and subsequent level off RA.

they too had a slight over speed due to a late disconnect of the A/T. 

 

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5 hours ago, Driverab330 said:

There was an event similar to what you had encountered actually had happened to one of our company 777 takin off from SFO a few years back. 

They were climbing out from 28L and there was a VFR traffic crossing their flight path at ~3000ft which generated a descend and subsequent level off RA.

they too had a slight over speed due to a late disconnect of the A/T. 

You mean this one?

 

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Not this one, but very similar.

This is a known problem for SFO for allowing VFR traffic into the departing corridor of a big international airport. 

 

 

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The good (since educating) thing about this is that I had recorded this event and now managed to form a video out of this that I uploaded to Youtube. Also I didn't know how to use the clock I think... Line-up is at 4:20, the traffic aural starts at 5:57.

 

Unfortunately, I deleted the corresponding savegame, but nonetheless I'll try to recreate that situation with your input in mind.

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On 16.9.2017 at 9:50 PM, CaptainLars said:

 

So I guess that I met the Flight Envelop Protection. Is it correct that the plane behaves that way? I would have expected such behaviour in an Airbus, not in a Boeing. Would it have been possible to take *more* control of the aircraft by deactivating Flight Director and switching A/T totally off? A/P wasn't on after all.

I'd appreciate any input on this situation... tbh, it was a bit scary! :ohmy:

 

The 777 is not a big friend of getting crashed and it will stay between spexific limits as soon as the pilot lets it. But, other than on an Airbus you are able to go into overspeed or even stall the airplane. You can disarm the autorhrottoes on the MCP and you can turn off the primary flight computers on the overhead panel. Bit that is nothing you would ever do to avoid a collision. Turn of the AP and the AT and do what TCAS tells you, but still use your brain, all above on Flightsim. --> the other aircraft is going to fly straight on, it will do nothing to avoid the crash 😆

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Well do you not have a reflex?

As soon as i need to fly THAT maneuver i would automatically disengage the A/T and pull them full back o.O i wonder that you could even achieve this descent rate with N1 at 92% and flaps 5.

In that situation a use of speedbrakes would even make sense for recovery.

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I'm so glad you would automatically do that, especially after having read the recommendations here.

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1 hour ago, CaptainLars said:

I'm so glad you would automatically do that, especially after having read the recommendations here.

:laugh:

after all the autopilot is nothing else than a  regulating control unit. It takes given values and corrects them with actions to come back to a specific target. When you are fast and pitching down it will pitch up and reduce throttle. The 777 has some protection systems, but, as this aircraft is really huge and heavy with some insanely huge engines, it is incredibly slow in doing anything. I have learnt to fly on a c172 that was equipped with a simple autopilot that mostly refused to do what you want it to do and most of the time it was overcorrecting. So as soon as you weren‘t absolutely sure about this evil part of automation you disconnected it and flew the aircraft with your brain and muscles. And that is exactly what you do on a triple 7 or an A330 when your in doubt of any action your AP is doing. Switch off any automation immediately and correct the situation manually. You are not as precise as those autopilots, but you are a lot faster and a lot more intelligent... :cool:

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On 10/2/2017 at 3:11 AM, CaptainLars said:

I'm so glad you would automatically do that, especially after having read the recommendations here.

Yes i definitely do that?! who the word not allowed rushes with climb thrust in 3000 feet altitude to the ground??

Further would a decrease in thrust reduce your pitch angle dramatically... You should normally never go above +30 or -10 degrees....

The only reason would be a stall recovery or maybe a windshear escape procedure....

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10 hours ago, 30K said:

Yes i definitely do that?! who the word not allowed rushes with climb thrust in 3000 feet altitude to the ground??

Further would a decrease in thrust reduce your pitch angle dramatically... You should normally never go above +30 or -10 degrees....

The only reason would be a stall recovery or maybe a windshear escape procedure....

I didn't rush to the ground, infact I tried to level off first, but the TCAS system kept advising me to descend. I thought that the A/T would be able to reduce thrust sufficiently on its own, but honestly, with the TCAS system urging me to descend because of another aircraft being about to land on the cockpit roof within a matter of seconds, I didn't think about the A/T.

 

On 2.10.2017 at 4:33 AM, Ephedrin said:

:laugh:

after all the autopilot is nothing else than a  regulating control unit. It takes given values and corrects them with actions to come back to a specific target. When you are fast and pitching down it will pitch up and reduce throttle. The 777 has some protection systems, but, as this aircraft is really huge and heavy with some insanely huge engines, it is incredibly slow in doing anything. I have learnt to fly on a c172 that was equipped with a simple autopilot that mostly refused to do what you want it to do and most of the time it was overcorrecting. So as soon as you weren‘t absolutely sure about this evil part of automation you disconnected it and flew the aircraft with your brain and muscles. And that is exactly what you do on a triple 7 or an A330 when your in doubt of any action your AP is doing. Switch off any automation immediately and correct the situation manually. You are not as precise as those autopilots, but you are a lot faster and a lot more intelligent... :cool:

Thank you for your comment, much appreciated.

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