Question on takeoff, climb out, and altitude restrictions...

[Slick9 24]

hi all - what mode would you recommend if you were flying a manual departure (planning on flying manually to FL180) in a very lightly loaded T7 on a SID with NOT ABOVE, and NOT BELOW, and speed restrictions?

I used D-TO2 derate with VNAV coming out of KLAS on the PRFUM.4 departure from 25R with an empty 300ER, I busted the 7000B restriction @ ROPPR becuase she took off like the space shuttle.  I was expecting the engines to roll back as I got closer to the the altitude restriction but it didn't happen and by the time I forced the nose down, I was through 7000 FT.  One thing i did not do was enter the hard restriction on the MCP, I assumed that because the restrictions were present and accounted for on the LEGS page that VNAV would observe those restrictions and adjust the auto throttle accordingly, but we all know what happens with assumptions.  

I've flown this same departure with a heavily loaded 200LR in VNAV mode in autopilot and all restrictions were obeyed, so I'm wondering if it's better to use FLCH mode for manual flight when the aircraft is light and there are NOT ABOVE restrictions to deal with.

thnx for any ideas

 

Richard Bansa

[scandinavian13 5,192]

5 minutes ago, Slick9 said:

I used D-TO2 derate with VNAV coming out of KLAS on the PRFUM.4 departure from 25R with an empty 300ER, I busted the 7000B restriction @ ROPPR becuase she took off like the space shuttle.  I was expecting the engines to roll back as I got closer to the the altitude restriction but it didn't happen and by the time I forced the nose down, I was through 7000 FT.  One thing i did not do was enter the hard restriction on the MCP, I assumed that because the restrictions were present and accounted for on the LEGS page that VNAV would observe those restrictions and adjust the auto throttle accordingly, but we all know what happens with assumptions.  

VNAV - if it busted the altitude requirement, I'm willing to bet there's something else at play here.

[Slick9 24]

Hi Kyle - I wouldn't be surprised if I had screwed something else up.  But then I thought maybe VNAV wasn't designed for an empty 777 that was being flown manually on auto throttle.  I guess that's another option, just turn off the autothrottle until I'm clear of restrictions.

Richard Bansa

[xkoote 57]

I believe that the autopilot couldn't keep up. It's a software and it has limitations. On the real aircraft operators usually set the restriction, until it is assured that it will be complied with by VNAV. However it is not a requirement for VNAV to have the hard altitude set in addition to the FMC programmed restriction.

I have flow empty 777 freighters, and reached FL390 12 minutes after takeoff. This airplane is a beast. To isolate weather it was user error, did your FMA switch to VNAV ALT? At these rates of climb, capture occurs 2000-3000 feet before the restriction. If it switched and busted anyways, I would chalk it up to software limitations.

What I would recommend you do next time is to switch to V/S. The speed window will open to the last FMC set speed (1. Flap placard -5 kts, or 2. FMC speed restriction for the active SID waypoint, or 3. 250 knots if the flaps have been retracted already and no speed restrictions exist). Reduce V/S to 2000 fpm or below and set speed accordingly.

The only thing is that now YOU are resposible for meeting the restriction if you choose not to have the MCP set at the restriction altitude. But that is what we are there for right?

 

Enjoy!

[Slick9 24]

Hi Xander -

The FMA did switch to VNAV ALT, but the climb was so fast, I was mashing the nose down trim and trying to kill the VS and boom I was through 7000 and still climbing.  

I'll give your V/S method a shot.  If i was in the real plane I would definitely not use autothrottle because after the blast off that I had, I'd be scared to death of altitude restriction violations.  I guess I'd have better training too though.

 

Richard Bansa

[downscc 1,327]

2 hours ago, Slick9 said:

Hi Xander -

The FMA did switch to VNAV ALT, but the climb was so fast, I was mashing the nose down trim and trying to kill the VS and boom I was through 7000 and still climbing.  

I'll give your V/S method a shot.  If i was in the real plane I would definitely not use autothrottle because after the blast off that I had, I'd be scared to death of altitude restriction violations.  I guess I'd have better training too though.

 

Richard Bansa

Keep in mind that those big GE's do not respond quickly to throttle changes.  There is a lot of angular momentum in those big engines.  When light, as Xander mentioned, the bird becomes a rocket.  You need to stay in front of it when faced with climb altitude restrictions.  Same thing happens at KLAX where missed approach altitude is only 2000 feet.... the automation will simply not cover every circumstance.

I am interested in that V/S was recommended.... there is no speed protection in this pitch mode so I'd be careful with its use.  I personally would hand fly the KLAS departure using FD in VNAV/LNAV modes to assist in this case, when heavy there's not a problem but when light look out. You don't want to bust that constraint because it is keeping you below the arrival traffic entering their downwinds.

[Driverab330 74]

13 hours ago, Slick9 said:

hi all - what mode would you recommend if you were flying a manual departure (planning on flying manually to FL180) in a very lightly loaded T7 on a SID with NOT ABOVE, and NOT BELOW, and speed restrictions?

I used D-TO2 derate with VNAV coming out of KLAS on the PRFUM.4 departure from 25R with an empty 300ER, I busted the 7000B restriction @ ROPPR becuase she took off like the space shuttle.  I was expecting the engines to roll back as I got closer to the the altitude restriction but it didn't happen and by the time I forced the nose down, I was through 7000 FT.  One thing i did not do was enter the hard restriction on the MCP, I assumed that because the restrictions were present and accounted for on the LEGS page that VNAV would observe those restrictions and adjust the auto throttle accordingly, but we all know what happens with assumptions.  

I've flown this same departure with a heavily loaded 200LR in VNAV mode in autopilot and all restrictions were obeyed, so I'm wondering if it's better to use FLCH mode for manual flight when the aircraft is light and there are NOT ABOVE restrictions to deal with.

thnx for any ideas

 

Richard Bansa

 

When one takes into account the airport elevation of KLAS is ~2181ft, an level off altitude of 7000ft only means there is just 5000ft of climb for the airplane to go before ALT capture. 

 

Having recently did a real ferry flight on the 773ER at 186tons take off (But the 772LR at the ferry flight weight will be even lighter with lower empty weight than the 773ER), I am quite happy to share some thoughts about this. 

 

With the AP engage, for an altitude about 7000ft (in your case just 5000ft AGL), it is less likely for the VNAV to overshoot because it will transition to Altitude capture mode at around 4000 to 5000ft and then the AP will slowly pitch down to level off. 

 

The pitch control of the AP on the real airplane is very slow to respond and it is tuned for passenger comfort, it is therefore quite common for an altitude bust if you have a low initial level off altitude like 2000-3000ft (normally the AP overshoots by about 200ft in most cases, but still within the IFR limit of 300ft) because you would still have the TO thrust until at least 1000ft AAL and by the time you select Flap 1 for CLB thrust to be selected you will be close to 2000ft already, although by then the mode would have changed to SPD VNAV ALT (or PATH depends on the coding)

The other interesting note is that with TO2-56 Take off thrust, on the 773ER, the thrust provided by CLB-2 is actually higher than the Take off thrust. So you will see your Rate Of Climb to trend up after CLb 2 is set. 

The rate of climb for a ferry flight weight (186TONS take off with ~175tons empty weight) 773ER before Thrust reduction was about 3200ft/Min and after clb2 is set it went to 3600-3900ft/min. Compared to a normal Rate of climb which is about 2000-2500ft after take off and around 1500-2200ft after thrust reduction. 

For my ferry flight, I managed to hand fly the airplane to about 15000ft staying in VNAV mode most of the time except two occasions. 

There was an ATC intermediate altitude restriction of 9000ft over a waypoint, as I approached about 6000ft I asked PM for V/S +1000(As other had previously suggested above). That way it slow things down dramatically and allows you to relax. 

 

The other trick (if you are doing it outside USA) is to request high speed after airborne. So once you clean up and above the MSA and terrain is not a problem just wind the speed up to 320kts, this will also slows down the rate of climb as well, couple with active use of V/S mode to manage the climb. 

 

I would still recommend to use the above technique even with the autopilot engaged. It just makes the life a a bit easier, as normal line pilot don’t really get to see this type of sporty action from the airplane that often. 

 

In addition, sometimes ATC will also get nervous as they see you zooming up on the radar if they have a quite few over fly traffic the area. 

 

The worse is not a ferry flight. The worst is that you have to go a full TO thrust take off out of an airport with F20 at 210tons on a normal passenger flight (like an 1:20hr trip from Tai pei to Hong Kong) because someone reported a windshear event on departure.

You get airborne, already climbing like a rocket and found out that the windshear was +20kts.... and now because the PM couldnt get a word in with the departure controller because the frequency is so busy, you need to level off at 3000ft as required by the SID. 

In this case I just use the Autopilot straight away at 200ft. There are days when there are so many threats to deal with and it is just not worth “flying” the airplane at all. 

[Driverab330 74]

13 hours ago, Slick9 said:

Hi Kyle - I wouldn't be surprised if I had screwed something else up.  But then I thought maybe VNAV wasn't designed for an empty 777 that was being flown manually on auto throttle.  I guess that's another option, just turn off the autothrottle until I'm clear of restrictions.

Richard Bansa

 

It is designed to be hand flown as well, but since a lot of times the VNAV on the real airplane will overshoot 10-30ft on altitude capture any way, as a good pilot if you to want fly accurately in altitude you will inevitably have to be “leading” the flight director in pitch mode a bit by reference to raw data, this will come by with some experience to, if done perfectly it will look like you are closely follow the FD but in effect it was the FD following you in pitch mode.

 

for example once you get SPD VNAV path / VNAV ALT / ALT, you may pitch down slightly lower to get a lower V/S first.

Because sometimes the FD will not command a level until you are 90ft from the target altitude while still doing 1000ft/min Rate or climb or descend. In that case if you are following the FD, there will be some delay between the actual FD command level and your control input, and further delay until the airplane actually respond to your control input. 

 

Therefore in in the case you are almost bound to overshoot the target altitude, especially with a high rate of climb of 2000-3000ft/min. 

In this case, if you prefer to hand fly, just pitch down using raw date as you arppaoch your target altitude but wait until the mode changes from “THR REF VNAV SPD” to “SPD VNAV PATH or VNAV ALT or ALT”.

It is because you don’t want to pitch down too early with the Autothrottle still commanding CLB thrust, otherwise the speed will go up. 

 

Once the A/T mode changes to speed, your speed is being look after, then it will be ok to depart from the pitch of the FD a little bit to anticipate the level off.

 

To practice just flying a few raw data climb or descend to a level off just like a IFR student pilot, you will get a feel of it. 

 

The 10% rule usually work (I.e for a 1000ft/Min rate of climb or descend, begin to level off 100ft before target altitude), may be allow 50ft more initially for a smooth level off to impress the passengers. 

 

For the 777 if you really want the pax to feel nothing, at 2000ft/min rate of climb you should begin your level off smoothly and slowly at around 300ft below / above target altitude and to reduce the vertical speed to 1000ft/Min approaching 100ft before target then apply the above technique. 

 

After some practice it will be one very nice smooth continuous action, even better than the autopilot. 

[CaptainGabe 81]

Simply sounds like you entered a strange scenario the plane never had seen before and it panicked. Low CI profiles should help the VNAV determine the climb profile based off of weight in a joint calculation with your thrust setting in the perf page before departure. Performance calculators are usually used before engine start to determine the best/preferred. It could also just be a hidden bug triggered by specific setups. 

[downscc 1,327]

12 hours ago, Driverab330 said:

The other trick (if you are doing it outside USA) is to request high speed after airborne. So once you clean up and above the MSA and terrain is not a problem just wind the speed up to 320kts

This is an interesting idea..... it would probably be approved given traffic conditions were okay at Las Vegas, where departure is used to handling the high speed fighter traffic at Nellis AFB and the range.