How to control climb rate after TO w/ VNAV enabled

[skelsey 765]

Hi Matthew,

 

Deleting the speed restriction below 10000' on the VNAV CLB page saves gas, is more comfortable and does not strictly contravene the laws of aviation even in FAA controlled areas. Just look at minimum manoeuvre plus fifteen at max TOW on the -W.

 

I'm very happy to be corrected -- but I was of the impression that the 250KIAS below 10,000 was very much the law in FAA-land (within 12NM of the coast in any case).

 

 

 

§91.117   Aircraft speed.

(a) Unless otherwise authorized by the Administrator, no person may operate an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots (288 m.p.h.).

( B) Unless otherwise authorized or required by ATC, no person may operate an aircraft at or below 2,500 feet above the surface within 4 nautical miles of the primary airport of a Class C or Class D airspace area at an indicated airspeed of more than 200 knots (230 mph.). This paragraph ( B) does not apply to any operations within a Class B airspace area. Such operations shall comply with paragraph (a) of this section.

© No person may operate an aircraft in the airspace underlying a Class B airspace area designated for an airport or in a VFR corridor designated through such a Class B airspace area, at an indicated airspeed of more than 200 knots (230 mph).

(d) If the minimum safe airspeed for any particular operation is greater than the maximum speed prescribed in this section, the aircraft may be operated at that minimum speed.

 

I was of the impression, from everything that I've read that ATC, in the US, is not the Administrator and cannot legally authorise >250KIAS (or min clean as outlined in (d)) below 10k except in specific circumstances where this has been pre-approved by the FAA (DFW springs to mind as somewhere where I believe the FAA has authorised high-speed departures).

 

Paragraph (d) takes care of the minimum clean speed issue with heavies.

 

In Europe, on the other hand, ATC is permitted to lift the restriction (and it does of course save time and fuel).

 

As I say, though -- very happy to be corrected -- always interesting to see how things differ between authorities!

[scandinavian13 5,192]

 

 

As I say, though -- very happy to be corrected -- always interesting to see how things differ between authorities!

 

Unless the plane (FMC) lifts the restriction by itself due to the min safe airspeed being higher than 250, here in the United States, you're busting a reg. The FMC, when at high gross weights, will command a speed higher than 250 when necessary. This is legal per 91.117(d).

 

Deleting it when the FMC leaves it in there and you're breaking a reg.

 

Granted, ATC probably won't even notice since the speed is usually only marginally above 250, but it's best not to go messing with things when you shouldn't be.

 

[skelsey 765]

Thanks Kyle, that was how I understood it.

[albertz 0]

I stand corrected with my generalisation especially regarding deleting the speed trans line and the direct mention of the FAA controlled areas.

I am aware of the regulation 91.117 but I think it is important to remember that the regs are black and white and aviation is seldom thus.

The phrase, minimum safe airspeed is totally judgemental and in no way implies -UP speed. Many 744 operators, for example, specify -UP +10 as minimum speed. For the T7 boeing refers to keeping minimum manoeuvre speed plus fifteen at all times (the behaviour of the MMS is another topic), no mention is made of non normal situations, windshear, turbulence etc.

Also in nearly all areas I am familiar with (excluding USA, The Bahamas, Bermuda, Transport Canada, Saudi?) the speed trans line can be deleted with approval to improve the mid level climb conditions so aside from the mention of FAA and T. Can the majority of the other 190 something countries stand by my reply, which, by the way, was intended to assist a generic (i.e. not land specific) question about passenger (albeit fictional / badly coded ones) comfort.

So in short i apologise for mentioning regs, the FAA, and I appreciate the correction for the benefit of both my future posts and others reading. I do sleep easily at night though, without fear of a fed in a grey suit coming after me next time I depart IAH on a heavily loaded T7 be it in RL or especially in a sim.

And finally it is I that is very happy to be corrected, If nothing else, one person is a little wiser today than yesterday, and that exemplifies the spirit of the forum and flight simulation in general.

Cheers

Matthew Knight

[qqwertz 770]

To be blunt, you're bending your flying to a product that isn't coded to be realistic. FSCaptain might add a feeling that things are more realistic because you have to follow procedures, but many add-ons that watch your vertical speed (to include FS2Crew) are hopelessly incorrect when it comes to penalizing or warning you for it.

 

People do not feel rate, they feel acceleration. The same way you feel natural going 450 knots through the air in a 777, you feel natural in a 5500 feet per minute climb/descent.

I beg to differ. You are right that people feel acceleration rather than rate, but they also feel the direction of acceleration. If you are climbing at 5500 ft/min then the angle the plane makes with the ground is rather steep and people will feel uncomfortable.

 

I have done some digging through the web. From what appears to be comments from RW 777 pilots I got the impression that the plane is indeed capable of a 6000 ft/min climb, but that normal rates are more like 3000 ft/min.

 

Btw, FSCaptain does not penalize pilots for climbing at 5500 ft/min with this plane, for the simple reason that this is how PMDG programmed it. With any other plane it would.

 

Peter

[scandinavian13 5,192]

 

 

The phrase, minimum safe airspeed is totally judgemental and in no way implies -UP speed. Many 744 operators, for example, specify -UP +10 as minimum speed. For the T7 boeing refers to keeping minimum manoeuvre speed plus fifteen at all times (the behaviour of the MMS is another topic), no mention is made of non normal situations, windshear, turbulence etc.

 

Right, but this would be addressed by 91.117a. The operator's definitions of things would be in a Company OpSpec. This OpSpec gets approved by the FAA and becomes enforceable as though they were regs, but the approval by the FAA carries...? You guessed it: the authorization of the Administrator.

 

 

 

And finally it is I that is very happy to be corrected, If nothing else, one person is a little wiser today than yesterday, and that exemplifies the spirit of the forum and flight simulation in general.

 

Glad you look at it that way. I've never come across anything so contentious as the speed argument. I've had lots of people get very angry when I pull the regs out on them.

 

 

 

I beg to differ. You are right that people feel acceleration rather than rate, but they also feel the direction of acceleration. If you are climbing at 5500 ft/min then the angle the plane makes with the ground is rather steep and people will feel uncomfortable.

I have done some digging through the web. From what appears to be comments from RW 777 pilots I got the impression that the plane is indeed capable of a 6000 ft/min climb, but that normal rates are more like 3000 ft/min.

 

Yes and no. Sure, people feel the direction of the acceleration, but sensation is partially dependent on position reference. This is best referenced to turbulence. During turbulence, people often "sense" that they're dropping hundreds of feet, when in fact, they're only dropping a handful. With limited reference points, their sensations are distorted. While you're right that someone can feel the angle between them and the force of gravity, this is not a refined sense (unless the person were blind, where other senses become heightened to compensate). They'd certainly feel it, but the difference between "climb" and "steeper climb" is likely lost on all of them.

 

Moreover, you're referring to posts of "RW pilots." While I usually question those posts in general (because anyone can say "RW Pilot" and go appear knowledgeable by reading an FCOM), I'll assume they were correct in saying what they say. However, those were real pilots, flying the aircraft to real SOPs (which is not the case in this thread). These SOPs and dispatch numbers likely come down from highers up dictating a certain procedure, such as the utilization of climb derates, to tame the climb. It's going to depend on the company.

 

 

 

Btw, FSCaptain does not penalize pilots for climbing at 5500 ft/min with this plane, for the simple reason that this is how PMDG programmed it. With any other plane it would.

 

Again, it shouldn't - regardless of the plane. The concept of hawkeyeing V/S is misguided in its entirety. Some airports require some pretty steep departure profiles (LGA, EGLC, to name a couple common ones - and SNA is certainly one), which would require those kinds of climb rates from other types of aircraft. Having been in aircraft departing like this, the feeling is "new" and not "uncomfortable."

[qqwertz 770]

Hi Kyle,

 

[About FSCaptain] The concept of hawkeyeing V/S is misguided in its entirety.

Well, the idea in FSCaptain is more like looking for the steepness of the angle. If you are climbing at 5500 ft/min at 250 Kts then the angle is approximately twice the one at 3000 ft/min. And of course there are individual ft/min rates in FSCaptain for each plane. I agree that the rate itself is meaningless, but if you combine it with the standard speed of a plane during climb, then you get something meaningful.

 

Your signature suggests that you have been on the development team, so you could perhaps enlighten us as to where the 5500 ft/min originate from. Surely you had a reason. I could imagine that this is the usual rate for the freighter, for instance.

 

Just to make this clear: I never had an issue with this climb rate, but it always stroke me as exceptional. Now that we're having this discussion it would be nice to learn more about it.

 

Best,

Peter

[scandinavian13 5,192]

 

 

Well, the idea in FSCaptain is more like looking for the steepness of the angle. If you are climbing at 5500 ft/min at 250 Kts then the angle is approximately twice the one at 3000 ft/min. And of course there are individual ft/min rates in FSCaptain for each plane. I agree that the rate itself is meaningless, but if you combine it with the standard speed of a plane during climb, then you get something meaningful.

 

That makes a little more sense, I guess. The pitch is more of what's being sensed, but still, unless you're been flying for years and years and years, the difference really isn't noticeable because most passengers don't have a frame of reference (even at a window seat). Moreover, they have no other experiences to compare it to outside of aviation. So, to those passengers, it's hard to say that this feeling is normal or abnormal in general. It's just sensory overload: the accel on the runway, the pitch up, the shaking of the airframe, the loud noises, and so on.

 

 

 

Your signature suggests that you have been on the development team, so you could perhaps enlighten us as to where the 5500 ft/min originate from. Surely you had a reason. I could imagine that this is the usual rate for the freighter, for instance.

 

Ah...I think I see the issue.

 

So, when it comes to departure (all the way up to cruise, in fact), your pitch mode is primarily a pitch-for-speed mode. This means that you set your engines at whatever setting you're going to set them, and then control your speed by adjusting pitch. If you're light, you're going to have to keep the pitch pretty high because of all of the excess thrust versus a very heavy departure. If you're heavy, you'll have a markedly lower V/S. In other words, you're using pitch to eliminate the excess thrust of the engine. For decreases in weight, you will have an increase in the pitch required to negate that thrust.

 

We didn't set the plane to look for a 5,500fpm climb rate. Rather, we set the plane to look for a way to hold the assigned speed (per the Boeing climb schedule, mind you) by modulating pitch. This is something that people do as far down as Cessnas, by the way.

 

This, of course, reflects my earlier point that RW pilots operate the aircraft to realistic procedures and numbers. A RW pilot and dispatcher would know that an aircraft at lighter weights should probably get a de-rate (or assumed temp) on takeoff to tame the pitch angle if they deemed it necessary. At light weight, the 777 will easily vault skyward with seemingly reckless abandon (try it: zero payload, 20,000lbs of fuel, no derate, fly it up via VNAV). You are correct, though, that freight carriers consider derates for comfort less than a passenger line would, but it's honestly not as much of a big deal as it's made out to be.

 

Seriously, the SNA departure is no joke (no derates and a standing run up used here):

[qqwertz 770]

Thanks for the explanations, Kyle. This makes a lot of sense to me and is most appreciated

 

Peter

[albertz 0]

Quick additional question to your last, informative answer. Regarding juristiction, do these approvals apply to us registered aircraft, us built aircraft or any aircraft operating over the us?

In the latter case, I imagine that the approval of domestic authorities would in most cases simply be ratified by the faa, leaving capacity for marginal authorities to be properly vetted.

The example that springs to mind is the case of the 744 leaving the west coast for London and having an engine failure. The faa were pressing that the airline was responsible for a regulation breach but the company's policy specifies to continue as the crew did. That policy must also have fallen under these criteria and been approved.

Similarly the us's argument that the eu has no juristiction over us registered aircraft's carbon output within eu airspace (that was always a ridiculous proposal on the part of fritz and his gang) is somewhat hypocritical if they are assuming juristiction for all operations within faa airspace, unless of course an incident or accident should occur.

Not really on topic but an interesting discussion.

Thanks again

Cheers

Matthew Knight

[skelsey 765]

 

 

Regarding juristiction, do these approvals apply to us registered aircraft, us built aircraft or any aircraft operating over the us?
In the latter case, I imagine that the approval of domestic authorities would in most cases simply be ratified by the faa, leaving capacity for marginal authorities to be properly vetted.

 

As far as I'm aware, any aircraft operating within the US. You have to comply with the regulations of the state that you are operating in -- To give another example -- you couldn't rock up at JFK in a G-registered aircraft and expect to use European approach minima or instance, or turn up in China and use feet (or, to be more accurate, the RVSM system that the rest of the world uses rather than the nigh-on dangerous mixing of systems and units that is used over there). Certain things like fuel policies etc are ratified by the various agencies -- hence why there are different rules in the USA for domestic and international flights -- but the basic 'rules of the air' are applicable to everybody or it would be chaos!

 

The difference in the "high speed" case is that in the UK, Europe and most (if not all) of the rest of the world, ATC are permitted to lift the 250kts below 10k/FL100 restriction, whereas in the States, a controller cannot legally do so (except at specific airfields where high-speed operations have been approved by the FAA).

 

From a pilot's point of view, the default position anywhere in the world is that you fly 250kts or minimum clean below 10k/FL100 unless you have a specific clearance from ATC to do otherwise. In the US, you won't be offered that, and if you ask for it you'll be turned down, because the controller is not legally able to lift the restriction.

 

In the case of the BA 747 -- I'm not really sure what the FAA's beef was, if I'm honest. To quote their own advisory (120-42B):

 

 

 

© If no more than one engine is shut down on an airplane that has three or more engines, § 121.565 permits the PIC to fly beyond the nearest suitable airport in point of time if the PIC determines that doing so is as safe as landing at the nearest suitable airport.

 

This is probably (certainly) not the place for a discussion on the merits of flight continuation policies for quads, but suffice to say that a 747 on three engines still has one more than a 777 with its full complement.

Incidentally, on the topic of climb rates -- pitch attitude for most types in my experience is generally limited (either by FCOM or company SOP) to a maximum of 20 degrees. The theory being that you pitch for V2+10 in the initial climb, but only up to 20 degrees nose-up -- if you get that far, you just accept the speed increase. The reason, from memory, is usually to do with what might happen if you were to lose a donk at an extreme nose-up attitude and low airspeed (and relatively low altitude).

 

There are other issues around climb rates in busy airspace -- mainly that if you go hurtling up towards your cleared level at 6000fpm you're liable to generate a TCAS RA for an aircraft above you. For this reason it's sensible (and indeed mandated many cases) to reduce the climb (or descent) rate approaching your cleared level (usually no more than around 1000fpm within 1000ft of cleared level).

[scandinavian13 5,192]

 

 

There are other issues around climb rates in busy airspace -- mainly that if you go hurtling up towards your cleared level at 6000fpm you're liable to generate a TCAS RA for an aircraft above you. For this reason it's sensible (and indeed mandated many cases) to reduce the climb (or descent) rate approaching your cleared level (usually no more than around 1000fpm within 1000ft of cleared level).

 

Yep. Additionally - and I haven't acknowledged this part yet - the initial altitudes being so low at certain airports (IAD is only 3000) would also call for some heavy derates to avoid rocketing through them, or abrupt pitch-overs to avoid busting them.

 

Great post overall, by the way.

[Budbud 227]

Hi,

 

I'm bringing back that thread to surface to ask something about common RW practice regarding climb at low weight.

For a short hop with low fuel, the T7 even at CLB2 can climb awfully quick in VNAV... I just tried it on flight with the -200LRF with 30T of cargo and 15T of fuel. At CLB2 derate the initial climb at 250kt was 4800fpm.

 

My question is not how to control the climb rate but rather what usually real pilots do in this case. Do company sets maximum climb rates in their SOP? (e.g.: max 3500fpm) or do they let their pilots manage the situation on their way?

 

The matters of comfort have been discussed already though one factor has not be expressed, the affect of the quick change of pressure in the ears.

 

Saying that with CLB2 derate the aircraft would still climb at 5500fpm, would you reduce the climb rate using V/S (or reducing the thrust manually) or would you let the aircraft do in VNAV?

 

I can remember an Air France flight from Paris to Port Harcourt via Lagos (Nigeria). The last leg took 1 hour in the continuity of the first one with a half full aircraft (in pax number). I tried to reproduce the flight (though I didn't get the weight of the cargo and the fuel remaining at Lagos, but assessing that they didn't tanker fuel) and got a quite high rate of climb for the last part. However in the real flight the climb felt really smooth and not harder that the first climb at Paris.

 

I know that the example is quite poor because of the lack of real information and numbered values but it is to illustrate my question.

 

I'm just curious to know what pilots do RW in order to improve the realism of my flight in FSX.

 

Thanks.

[scandinavian13 5,192]

 

 

My question is not how to control the climb rate but rather what usually real pilots do in this case. Do company sets maximum climb rates in their SOP? (e.g.: max 3500fpm) or do they let their pilots manage the situation on their way?

 

For some reason, the sim community seems to be hung up on climb and descent rate, and it's really not what they think it is. Climbs and descents are measured in distance over time (feet per minute, in most cases). Another metric that uses these parameters is airspeed, which is also distance over time (nautical miles per hour, or knots, in most cases). I'll get to the ear point in a moment, but I'm going over this part for anyone else who comes by this post.

 

If it were true that high speed was somehow uncomfortable, or odd, then passengers who are used to walking, using the train, and driving would be sitting in the back of a 747 thinking OH MY GOD WE'RE GOING TO DIE!!! Those who flew Concorde would, of course, simply be scared to literal death at just over twice that speed. As you read those last statements, though, you immediately thought "but no, that's not the case. Passengers wouldn't feel the difference, really."

 

People do not feel speed - they feel acceleration. You don't feel that you're moving at a certain speed to tell that you're moving. You simply feel the minor accelerations of the imperfections in the road, track, or air to tell you're still moving, but you cannot feel the difference between 400 knots any more than you could 600 knots without some other sign (vibrations, louder slipstream noise, and so on).

 

From there, all anyone needs to do is connect the fact that vertical speed is a speed, which means it is not felt. The only way someone could tell vertical speed would be if they were keenly aware of the gravity vector between the normal "straight down the spine" position, and the current pitch, but very few people have a sense that keen, so that change from the norm is only seen as "I can tell I'm going up/down." You have likely been in aircraft where there was a climb or descent made at 2000 fpm, but likely also one made at 4000-5000. The thing is, you likely can't recall which one it was. In fact, I'm willing to bet that if the data were available to verify, you wouldn't be able to pick which one it was, but would select a different one based on the actual acceleration force: the rate of change from level flight, to climbing/descending flight. An abrupt pitch change is something people feel, which would likely make them identify a flight as one with a rapid descent, even if the vertical speed was tame.

 

So, all of that being said, this concentration on the idea that someone would artificially cap vertical speed is predominantly misguided. Granted, if the crew knows there is a short climb from one level to another, that climb likely wouldn't be made on the thrust limiters. Instead, if going from 14000 to 16000, a pilot might use FL CH (which modulates the thrust for short climbs like that), or speed plus V/S. If climbing from 3000 to 16000, however, it can be left in VNAV and whatever resultant V/S won't be felt by the passengers, apart from the rate of the change in pitch, initially.

 

 

 

The matters of comfort have been discussed already though one factor has not be expressed, the affect of the quick change of pressure in the ears.

 

This has been addressed here, though not as commonly. This isn't so much dependent on the rate of ascent as much as it's on the ability of the pressurization to keep up, along with the max pressure differential of the hull. I think this side of the simism came mainly from the fact that most pressurization functions in simulators are mostly or fully automated for the aircraft people are using in the sim (when the DC-6 comes out, have fun  ).

 

The ability to maintain a particular cabin altitude comes from the structural strength of the airframe, which is limited to a max pressure differential. If one were to watch the pressurization gauge in the DC-6 as you roll the flight altitude up, one would see the cabin altitude remain at zero until the gauge hits that max differential, and then it would drag the cabin alt indicator up behind it. In theory, I could operate the DC-6 at 6000 with the cabin altitude at 0, or I could operate it with the cabin altitude set to 6000 (unpressurized).

 

Now that the altitude portion is covered, we move on to the change between those altitudes. Unlike people's sense of movement on the body (based on change in rate over time), pressurization is a sense that is felt based on rate alone. The rate of change, as I'm sure you've noted, is the big issue here. Since I can operate the DC-6 at 6000 with a cabin altitude of 0, I could climb at a high rate between 0 and 6000 without the passengers even feeling a change in pressure. I could also climb at a high rate between those altitudes with the cabin altitude set to 1000, and the pressure controller would slowly let the pressure up during that change (you could adjust the rate limiter to a point where it lets the altitude up so slowly that it's doing so even after you reach cruise - the 6 manual also goes into techniques to ensure the alt climbs/descends through intermediate level offs as well). Again, people wouldn't notice the slow rate to 1000 much. As long as you do not exceed the max pressure differential, you can set a rate on the cabin altitude (climb or descent) such that you could have a very fast climb without an uncomfortable pressure change.

 

Finally. the climb wouldn't really be the uncomfortable part anyway, even if the actual pressure change was higher. It would be the descent where more pain would be felt. Fly with a stuffed up head after having a cold and you'll know what I'm talking about: the way up isn't bad as most of the result is that you just can't hear as well from the pressure loss causing a differential on the low side; the descent is where the added pressure increasing the pressure differential causes pain. The pain causing side (descent) isn't quite the same, performance-wise, as it doesn't have as much to do with thrust and weight. That is to say, a light 777 might rocket up to altitude, but the descent can still be made relatively normally.

[Budbud 227]

Well I had perfectly understood the matter regarding the difference between rate of climb and acceleration since the first post.

 

My concern was focussed on the pressurization and the effect of the rapid change of pressure on the organism and you clearly answered it on the second part of your post above.

 

So the lesson to learn for me is that high rate of climb is not an issue on the pressurization side and there is no limitation or special recommendation on the rate of climb (in normal situation) neither on SOPs or anything else.

 

The only think to avoid is the accelerations due to brutal changes of pitch during climb. So as I understand rate of climb above 3500fpm or 4000fpm may not be so uncommon for high-powered aircrafts at low weight such as B777 or B757.

 

Thanks for the documented answers as usual Kyle!