VNAV stepped climb/enhanced Mode S question
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VNAV stepped climb/enhanced Mode S question
Hello All,
Having programmed and checked the SID waypoints, speed restrictions and altitude restrictions, i.e. stepped climb, we can either:
1/ set the final level, e.g. 10 000' in the altitude preselector, set sail in LNAV/VNAV, carefully supervise the beast doing its thing and jump in if need be by, say, hitting ALT should we observe an altitude bust in the making thereby initiating a level-off.
2/ set the first level-off altitude, e.g. 4000' in the altitude preselector, blast off in LNAV/VNAV, monitor and adjust the altitude preselector to the next step-climb altitude when the VTA chime sounds, i.e. just prior to the thing actually remaining level at 4000' instead of continuing on up as per the SID.
I know that both techniques work just fine. (actually seen both taught in the sim) I actually prefer #1 because the great thing about LNAV/VNAV/autothrottles is that it frees up the driver to concentrate on monitoring more efficiently, and provided that FMS inputs are checked thoroughly prior to departure the aircraft (BD-700) will perform as advertised.
HOWEVER, just had a seasoned instructor tell me that setting the FINAL altitude in the preselector when performing a stepped climb will result in ATC getting worried as a result of enhanced Mode S, in other words ATC will see that we've set 10 000' and not the initial 4000' restriction and may suspect that we're intent on bombing straight up to 10 000'?
Any informed opinion out there much appreciated!
Regards
Having programmed and checked the SID waypoints, speed restrictions and altitude restrictions, i.e. stepped climb, we can either:
1/ set the final level, e.g. 10 000' in the altitude preselector, set sail in LNAV/VNAV, carefully supervise the beast doing its thing and jump in if need be by, say, hitting ALT should we observe an altitude bust in the making thereby initiating a level-off.
2/ set the first level-off altitude, e.g. 4000' in the altitude preselector, blast off in LNAV/VNAV, monitor and adjust the altitude preselector to the next step-climb altitude when the VTA chime sounds, i.e. just prior to the thing actually remaining level at 4000' instead of continuing on up as per the SID.
I know that both techniques work just fine. (actually seen both taught in the sim) I actually prefer #1 because the great thing about LNAV/VNAV/autothrottles is that it frees up the driver to concentrate on monitoring more efficiently, and provided that FMS inputs are checked thoroughly prior to departure the aircraft (BD-700) will perform as advertised.
HOWEVER, just had a seasoned instructor tell me that setting the FINAL altitude in the preselector when performing a stepped climb will result in ATC getting worried as a result of enhanced Mode S, in other words ATC will see that we've set 10 000' and not the initial 4000' restriction and may suspect that we're intent on bombing straight up to 10 000'?
Any informed opinion out there much appreciated!
Regards
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Personally 1 - ie set the cleared alt/FL and let VNAV take care of intermediate stop alts. I've never had ATC check on whether we intend to stop at the intermediate stop alt.
On a similar subject, a recommendation from the BA 777 accident report was that cruise step climbs should involve the use of full climb power - staying in VNAV for this will do just this but VS (as the BA used) - won't.
I've always used VNAV for step climbs because I have a vague memory of a notice that said that other aircraft's enhanced TCAS knows your stop altitude, so high rates of climb are not a problem when using VNAV (contrary to the belief of a few fellow pilots who chide me for not using VS). Does anyone remember this notice or did I imagine it? I also dont use VS in the climb for the simple reason that there is no speed floor protection.
On a similar subject, a recommendation from the BA 777 accident report was that cruise step climbs should involve the use of full climb power - staying in VNAV for this will do just this but VS (as the BA used) - won't.
I've always used VNAV for step climbs because I have a vague memory of a notice that said that other aircraft's enhanced TCAS knows your stop altitude, so high rates of climb are not a problem when using VNAV (contrary to the belief of a few fellow pilots who chide me for not using VS). Does anyone remember this notice or did I imagine it? I also dont use VS in the climb for the simple reason that there is no speed floor protection.
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Thanks, Timetraveller. We've never had any queries either, when doing so. Need to go speak to the spanners about the finer details, I guess. (Perhaps some info from a tinpusher out there?)
The pre-Batch II GLEX's would pitch the nose up and down nauseatingly when in FLC, which is why the use of VS became widespread. Not ideal as you mentioned, however it was deemed preferable to the pre-mod gyrations of FLC when VNAV was not an option due to vectors, etc.
The pre-Batch II GLEX's would pitch the nose up and down nauseatingly when in FLC, which is why the use of VS became widespread. Not ideal as you mentioned, however it was deemed preferable to the pre-mod gyrations of FLC when VNAV was not an option due to vectors, etc.
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Level Busts are a BIG THING in Europe, and corporate aviation has a bad name in this area.
It's all about confidence: if a controller gave you a descent clearance that you though took you close to the granite I'm sure you'd query it.
So showing on their radar the possibility that you're gonna zoom past your cleared climb limit must shurely be in the same bag?
If there's a way of making pilot work loads easier without increasing ATCos heart rate the everyone will be happy.
Sir George Cayley
It's all about confidence: if a controller gave you a descent clearance that you though took you close to the granite I'm sure you'd query it.
So showing on their radar the possibility that you're gonna zoom past your cleared climb limit must shurely be in the same bag?
If there's a way of making pilot work loads easier without increasing ATCos heart rate the everyone will be happy.
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Doodlebug...
Just a question, what happens if your vertical mode inadvertantly changed from VNAV to V/S unoticed (say from a FMC hiccup which changed the autopilot mode-You diagnosing the FMC...). Sailing through your cleared level? Do you use VNAV for an single engine climb? (so would you remember to change the altitude preselect window to the lower value shortly after an engine failure?). Just thinking of a few 'what ifs' thats all.
Second thing is tonight we had a 'mild' RA caused by another aircraft climbing to a level 1000' below us. Our V/S 500fpm (descending), the TA came when he was 3500' below us, the RA when he was 1700' below.... Enhanced mode S ain't as clever as all that...
And as for VNAV for stepped climbs, what happened to passenger comfort?
Just a question, what happens if your vertical mode inadvertantly changed from VNAV to V/S unoticed (say from a FMC hiccup which changed the autopilot mode-You diagnosing the FMC...). Sailing through your cleared level? Do you use VNAV for an single engine climb? (so would you remember to change the altitude preselect window to the lower value shortly after an engine failure?). Just thinking of a few 'what ifs' thats all.
Second thing is tonight we had a 'mild' RA caused by another aircraft climbing to a level 1000' below us. Our V/S 500fpm (descending), the TA came when he was 3500' below us, the RA when he was 1700' below.... Enhanced mode S ain't as clever as all that...
And as for VNAV for stepped climbs, what happened to passenger comfort?
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Hello Cough
Thanks for your thoughts.
Regarding your questions: I cannot think of a situation in which VNAV will change to VS in this phase of flight other than by a button being pushed, but then I'm sure someone will be along to point out what I'm forgetting in a minute? If, on the other hand, ATC were to give us a heading VNAV would obviously decouple on selection of HDG and the verticle profile would lapse into pitch mode. At which point you're no longer on the stepped-climb departure anyhow, and anyway ATC will always give you an altitude cleared to, in such a case, which will prompt you to reset the altitude preselected if necessary.
No, I wouldn't use VNAV on a single-engine climb, because when in an emergency I'd advise ATC and be allowed to fly whatever profile I'd have to in order to put the aircraft on the ground safely. In other words, I'd be off of the usual stepped climb SID and under vectors as an emergency aircraft, concentrating on reaching whatever acceleration altitude applies.
Passenger comfort is very high up on our list. (and believe me they wouldn't hold back!) No complaints from them about VNAV, ever. Works well, at least on our airframe.
Are you saying that you prefer not to use VNAV at all?
Thanks for your thoughts.
Regarding your questions: I cannot think of a situation in which VNAV will change to VS in this phase of flight other than by a button being pushed, but then I'm sure someone will be along to point out what I'm forgetting in a minute? If, on the other hand, ATC were to give us a heading VNAV would obviously decouple on selection of HDG and the verticle profile would lapse into pitch mode. At which point you're no longer on the stepped-climb departure anyhow, and anyway ATC will always give you an altitude cleared to, in such a case, which will prompt you to reset the altitude preselected if necessary.
No, I wouldn't use VNAV on a single-engine climb, because when in an emergency I'd advise ATC and be allowed to fly whatever profile I'd have to in order to put the aircraft on the ground safely. In other words, I'd be off of the usual stepped climb SID and under vectors as an emergency aircraft, concentrating on reaching whatever acceleration altitude applies.
Passenger comfort is very high up on our list. (and believe me they wouldn't hold back!) No complaints from them about VNAV, ever. Works well, at least on our airframe.
Are you saying that you prefer not to use VNAV at all?
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For me the problem with putting the intermediate stop in the window is that it requires the pilot to remember to reset the altitude once the intermediate stop is passed - and pilots are fallible - VNAV is pretty damn reliable and will fly the profile pretty much automatically.
A failure to resume climb after the intermediate stop is just as much as bust as is a climb through an altitiude.
NB I think the question is relevant to recent products from Boeing/Airbus, cos older types can put you in funny unexpected modes, (by knocking the pitch switch or changing pitch modes close to the level off, for example).
A failure to resume climb after the intermediate stop is just as much as bust as is a climb through an altitiude.
NB I think the question is relevant to recent products from Boeing/Airbus, cos older types can put you in funny unexpected modes, (by knocking the pitch switch or changing pitch modes close to the level off, for example).
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Doodlebug,
Like everything, I use a mode depending on what I am trying to achieve. In my book, using VNAV for small stepped climbs in a TMA I don't find appropriate (as I would be setting off other peoples TCAS and unnecessarily working the engines). Using VNAV for longer climbs with little other traffic around is totally appropriate. Curious that your type drops VNAV when in HDG (ours doesn't, provided that we are within a certain distance of the original track).
The other bit that is probably biasing my reply, is from my local airport the same thing happens daily. We blast off (on a stepped climb SID), contact departure freq and the first thing that the controller usually says is 'maintain altitude' which is normally the first stop. Thus we have negated the rest of the step climb SID. Also, the first step is normally underneath other traffic, so if I see other traffic locally, then I will revert to V/S mode with 1000' ft to go, to prevent TCAS problems.
For me, not setting off TCAS is a workload thing. Every time it goes RA, I have to reach for a MOR form and fill it out (later, obviously). I'm too lazy, so if I can, I try and avoid the RA's.
Safe flying dude...
Like everything, I use a mode depending on what I am trying to achieve. In my book, using VNAV for small stepped climbs in a TMA I don't find appropriate (as I would be setting off other peoples TCAS and unnecessarily working the engines). Using VNAV for longer climbs with little other traffic around is totally appropriate. Curious that your type drops VNAV when in HDG (ours doesn't, provided that we are within a certain distance of the original track).
The other bit that is probably biasing my reply, is from my local airport the same thing happens daily. We blast off (on a stepped climb SID), contact departure freq and the first thing that the controller usually says is 'maintain altitude' which is normally the first stop. Thus we have negated the rest of the step climb SID. Also, the first step is normally underneath other traffic, so if I see other traffic locally, then I will revert to V/S mode with 1000' ft to go, to prevent TCAS problems.
For me, not setting off TCAS is a workload thing. Every time it goes RA, I have to reach for a MOR form and fill it out (later, obviously). I'm too lazy, so if I can, I try and avoid the RA's.
Safe flying dude...
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The below is from my Flight Crew Training Manual (published by the manufacturer). The at-or-below paragraph is of interest. Using the technique below provides altitude alerting, and if I come out of VNAV while maneuvering around a buildup, or for any other reason, I will have altitude capture capability. I am in agreement with Cough in that circumstances will determine which mode I use.
Climb Constraints
Climb constraints may be automatically entered in the route when selecting a
procedure, or manually entered through CDU entry. When the airplane levels off
at an MCP altitude, that altitude is treated as a climb constraint by the FMC.
All hard altitude climb restrictions should be set in the MCP altitude window
including “at or below” constraints. The next altitude may be set when the
restriction has been satisfied, or further clearance has been received. This
procedure provides altitude alerting and assures compliance with altitude
clearance limits.
If VNAV is maintained as the active pitch mode throughout the climb, the highest
altitude restriction may be set in the MCP altitude window. The climb must be
monitored to ensure compliance with all altitude constraints. If at any time the
active pitch mode is changed from VNAV to any other climb mode (e.g. FLCH,
V/S, etc.), the next altitude restriction must be reset in the MCP altitude window.
Note: Use of CLB DIR deletes constraints from the LEGS page.
Climb Constraints
Climb constraints may be automatically entered in the route when selecting a
procedure, or manually entered through CDU entry. When the airplane levels off
at an MCP altitude, that altitude is treated as a climb constraint by the FMC.
All hard altitude climb restrictions should be set in the MCP altitude window
including “at or below” constraints. The next altitude may be set when the
restriction has been satisfied, or further clearance has been received. This
procedure provides altitude alerting and assures compliance with altitude
clearance limits.
If VNAV is maintained as the active pitch mode throughout the climb, the highest
altitude restriction may be set in the MCP altitude window. The climb must be
monitored to ensure compliance with all altitude constraints. If at any time the
active pitch mode is changed from VNAV to any other climb mode (e.g. FLCH,
V/S, etc.), the next altitude restriction must be reset in the MCP altitude window.
Note: Use of CLB DIR deletes constraints from the LEGS page.
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Thank you all, Gents, for good info.
None - brilliant, that settles that, the question regarding what ATC may or may not perceive has therefore just become a moot point. Thank you!
None - brilliant, that settles that, the question regarding what ATC may or may not perceive has therefore just become a moot point. Thank you!
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brilliant, that settles that
I think you would be better following guidance from your employer rather than someone on here. What you are discussing here is completely contrary to what my employer wants us to do in our B737, B757 and B767s and our procedures are all regulated by the JAA and Boeing.
Time Traveller
On a similar subject, a recommendation from the BA 777 accident report was that cruise step climbs should involve the use of full climb power - staying in VNAV for this will do just this but VS (as the BA used) - won't.
From the Interim Report
"The last high fuel flow demand on G‑YMMM prior to the approach into Heathrow, and when the main fuel tanks were supplying the engines, was during a VNAV commanded step climb on the previous flight into Beijing when the fuel flow reached 10,700 pph. The step climbs on the accident flight had both been completed in VS mode with a low rate of climb selected, which resulted in lower fuel flows."
Special Bulletin S03 states;
Operational changes
No operational changes are currently recommended by either the AAIB, Boeing or Rolls-Royce.
Please provide a quote from the report that backs up your statement. I can't see any recommendation there, only a statement of fact, but I can't get Special Bulletin S01 to open.......
Be careful thinking that what applies to one type applies also to another. Use of V/S for stepped climbs can be a suitable mode. Nowhere have I seen information that says you need to apply full climb power on any of the variants that I have flown (all Boeing). BUT, you need to be careful using V/S on a 75/6 when climbing, especially high in the envelope as there is no speed protection, whereas on the 73 there is.
PP
As for using VNAV to level off in a busy traffic environment, try reading about it here; http://www.eurocontrol.int/msa/galle...n_7_Mar-06.pdf read the bit on page 2 in yellow.
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My understanding is that, with the latest TCAS/Mode S fits, it doesn't happen, irrespective of rates of climb/desc. (I welcome being proved wrong on that though)
Rather the documentation tells us that exchange of altitude target is not an ACAS feature and won't be as RAs could be unable to provide a safe distance to another aircraft in the case of a level bust, therefore high rates are still discouraged. Which is of course represented in our SOPs with a max rate of 1500fpm for the last 1000ft outside RVSM and 1000fpm in the last 1000ft within RVSM airspace.
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Morning Pete
I did state the aircraft-type. Twice.
I accept nothing blindly, however I am always happy to receive input and to acknowledge same politely.
I did state the aircraft-type. Twice.
I accept nothing blindly, however I am always happy to receive input and to acknowledge same politely.
