[Jeroen]

Ok, here a detailled questions for the pro’s. Searchhaven at the beginning of this terrific post mentioned modes such as VNAV, V/S.

It is easily one of the most hotted discussed topic on many aviation forums. Which also suggest there might be one more correct answer. Just to add, lets have a go at FL CH as well.

I’m not sure how this works in an Airbus?

Anyway, VNAV, V/S and FL CH are different auto-modes with very different characteristics to get you from one altitude to a next altitude.

I have often discussed this with my KLM pilot friends. KLM prefers VNAV over any other vertical mode. The exception being descending under 10.000 feet. The reason FL CH is a little more predictable in what it does over VNAV. (I’m sure all pilots will have found themselves in a situation where VNAV puts you in a climb, whereas you thought you were going to descent)

Very little use for V/S as far as KLM is concerned. Maybe when doing a VOR approach where you need a fixed f/min descent rate.

My impression, also going by discussion on PRUNE forum, is that it is company specific and in some case down to individual preference.

The little planes I fly (mostly glas cockpits such as Diamonds and Cirrus) do have auto pilot. But there are no single piston engine planes on the market that have full auto throttle installed (no FADEC). So I do have a few vertical modes to play with along the usual LNAV, heading/course, but I will always need to watch my speed and engine settings separately. Climbing on V/S without watching airspeed will get you into trouble very quickly.

So can anybody enlighten me how your company, or personal preferences, defines the use of these three different vertical modes and why?

Thanks

Jeroen

[extreme_torque]

Oh man what a treasure trove of information for us mere mortals. I am throughly fascinated by these big birds and especially the jet engine. Thrust, engine size aside, I am still astonished everytime I see them take off or land. Infact just today I went bird spotting near the Melbourne Airport and caught one of the biggest of them all.. a Qantas Boeing 747

[searchingheaven]

Originally Posted by Jeroen

Anyway, VNAV, V/S and FL CH are different auto-modes with very different characteristics to get you from one altitude to a next altitude.

I have often discussed this with my KLM pilot friends. KLM prefers VNAV over any other vertical mode. The exception being descending under 10.000 feet. The reason FL CH is a little more predictable in what it does over VNAV. (I’m sure all pilots will have found themselves in a situation where VNAV puts you in a climb, whereas you thought you were going to descent)

VNAV: This is the FMC programmed vertical profile mode. VNAV engages above 400 feet after takeoff, if armed. A lot of operator use this preferentially. Any altitude restrictions are already present in the FMC. For example, when you take off from Kolkata VECC 01R, TEPAL waypoint has 14000B(below) restriction. So the FMC keeps you under 14000 till TEPAL, & then climbs up to the MCP altitude.

VNAV engages in the appropriate VNAV mode as required to maintain the current flight path:

• VNAV SPD – The AFDS maintains the FMC/MCP speed displayed on the PFD airspeed indicator.

• VNAV PTH – The AFDS maintains FMC altitude or descent path with pitch commands. If the MCP altitude window is set to the current cruise altitude as the airplane approaches the top of descent, the CDU scratchpad message RESET MCP ALT displays to tell you that it requires your permission to descend below the MCP altitude.

• VNAV ALT – When a conflict occurs between the VNAV profile and the MCP altitude, the airplane levels and the pitch flight mode annunciation becomes VNAV ALT. VNAV ALT maintains altitude. To continue the climb or descent, change the MCP altitude and push the altitude selector or change the pitch mode.

FLCH: FLCH stands for flight level change mode. Usually, we are cleared by the ATC to an initial climb altitude, and then on to our cruise altitude. So we enter the initial climb altitude into the MCP. This ensures that the autopilot does not cross the initial climb altitude in VNAV mode. Once ATC has cleared us to climb higher, we enter the new altitude in the MCP, and press FLCH. This disengages VNAV and the aircraft starts climbing to the new altitude in the MCP.

VS/FPA: Vertical Speed/Flight path angle mode makes the aircraft climb at a set vertical speed or angle. This is used in very rare cases to increase or decrease the climb/descent speed. FLCH mode maintains airspeed during a climb or descent, while VS mode maintains a specific vertical speed.

FLCH has speed protection because the speed set in the MCP window is the primary target, the airplane will adjust pitch to fly that speed regardless of engine thrust setting. However in V/S, vertical speed will be the primary target, if let say you set +4000 fpm to try to do a cruise climb close to the MAX altitude, the AP will command a 4000 fpm rate of climb in the expense of losing airspeed because airspeed can not be maintained at such a high rate of climb at high altitude. As result the speed will decrease to Vmms until the AP stall protection kick in to save the airplane.

Therefore FLCH is a good mode to use for most cruise altitude changes. V/S is best to use on at lower altitude to fine tune your descend profile, however it is rarely used.

Originally Posted by Jeroen

(I’m sure all pilots will have found themselves in a situation where VNAV puts you in a climb, whereas you thought you were going to descent)

I cannot speak for others, but it has not happened with me till now. Each mode is different from the other and their behavior is very predictable, if the PFD annunciations are interpreted correctly.

Originally Posted by Gansan

So I suppose only fuel can be thrown out. Are there any rules and regulations for doing that? Like you can't dump when you are over certain areas?

Fuel jettisoning is a procedure wherein excess fuel is dumped to reduce the landing weight of the aircraft in case of an emergency. The primary reason for this is that in case of a missed approach, the aircraft will not have enough power required to climb due to excess weight. Structurally, the aircrafts are designed with enough safety margins to land well above the landing weight. But the Missed Approach Performance(MAP) is the factor to consider. In smaller aircraft like the A320/B737, even 15 mins of flying will burn enough fuel to get the required MAP. However, the aircraft I fly, has 140,000 kgs of fuel on some routes. Hence the jettisoning feature.

In general, fuel jettisoned above 5,000 to 6,000 feet will completely vaporize before reaching the ground. Therefore, Boeing’s general recommendation is to jettison fuel above 5,000 to 6,000 feet whenever possible, although there is no restriction on jettisoning at lower altitudes if considered necessary by
the flight crew.

This is a photo of the 777 fuel jettison panel. Fuel jettison is initiated by pushing the FUEL JETTISON ARM switch to select ARMED. The jettison system automatically sets the fuel–to–remain to the maximum landing weight (MLW) fuel quantity.


Photo showing manual & auto modes. In auto mode, enough fuel is dumped to bring the aircraft to maximum landing weight. In manual mode, you can pull on and rotate the FUEL TO REMAIN selector to manually decrease or increase the TO REMAIN quantity. As a safety precaution, jettisoning nozzles cannot open on the ground, regardless of switch positions.

[Jeroen]

Originally Posted by searchingheaven

[
Therefore FLCH is a good mode to use for most cruise altitude changes. V/S is best to use on at lower altitude to fine tune your descend profile, however it is rarely used.
]

Why would you switch from VNAV to FLCH? In VNAV you are following whichever restrictions you have in the flight plan as per the inputs in the FMC AND whatever you have set up on the MCP.

So whatever you have set up in the MCP will be final. Why change to FLCH? Just dial in whatever altitude restriction you want, push the ALT and you will continue in VNAV.

i’m aware that there are some variants of FLCH mode floating around on Boeing fleets. But on the 744 I see most using VNAV for step climbs in cruise as well. The one exception seems to be if you are relatively low on weight.

Thanks

Jeroen

[searchingheaven]

The 777 is mainly flown in VNAV mode. FLCH is used in conditions where VNAV doesn't suit the demand. Using VNAV always provides you the full climb thrust. VNAV puts autothrottle in THR REF mode while FLCH used THR mode. If ATC clears me for small altitudes at a time, FLCH is preferred since it is very uncomfortable for us to climb in VNAV at full thrust for 5000 ft, level off and then climb again at full thrust for the next 5000 ft. FLCH feels much more gradual and smooth than VNAV.

In THR mode, the autothrottle applies thrust to maintain the vertical speed required by the pitch mode i.e just enough to maintain the required pitch angle for climb. While in THR REF mode, thrust is set to the selected thrust limit displayed on EICAS. Thus FLCH feels smoother than VNAV.

[sriramr9]

Few more questions from my end :
1. With so much automation is it still possible to fly the airplane manually by overriding auto pilot and shutting it off. Will it not give the pilots the real world experience to handle during crisis instead of synthetic feel?
2. Between joystick and yolk which is a more fool proof way of medium in terms of safety . I hear joystick handle independently does it not give birth to irrational inputs by both officers at same time ?
3' How does a aircraft successfully ground the residual voltage after a lightning strike despite no contact with earth?
4. In case of AF447 during violent descent did the deicing on pitot not happen?? In case of successful de icing of pitots theoretically the systems should resume back right as air speed will be available ??

[flyboy747]

Originally Posted by searchingheaven

The 777 is mainly flown in VNAV mode. FLCH is used in conditions where VNAV doesn't suit the demand. Using VNAV always provides you the full climb thrust. VNAV puts autothrottle in THR REF mode while FLCH used THR mode. If ATC clears me for small altitudes at a time, FLCH is preferred since it is very uncomfortable for us to climb in VNAV at full thrust for 5000 ft, level off and then climb again at full thrust for the next 5000 ft. FLCH feels much more gradual and smooth than VNAV.

While that is true, in cruise for a step climb of even 2000 feet, which is mostly the case, we stay on VNAV. The FLCH mode is used, as per my company policy only in descents below FL 100 and that too only if you are not doing a VNAV/LNAV approach.

Also, congratulations searchingheaven for an excellent review of the triple. Happy landings and tailwinds.

[Jeroen]

Originally Posted by searchingheaven

The 777 is mainly flown in VNAV mode. FLCH is used in conditions where VNAV doesn't suit the demand. Using VNAV always provides you the full climb thrust. VNAV puts autothrottle in THR REF mode while FLCH used THR mode. If ATC clears me for small altitudes at a time, FLCH is preferred since it is very uncomfortable for us to climb in VNAV at full thrust for 5000 ft, level off and then climb again at full thrust for the next 5000 ft. FLCH feels much more gradual and smooth than VNAV.

Originally Posted by flyboy747

While that is true, in cruise for a step climb of even 2000 feet, which is mostly the case, we stay on VNAV. The FLCH mode is used, as per my company policy only in descents below FL 100 and that too only if you are not doing a VNAV/LNAV approach.

thanks both of you.

I just ran a few scenario’s through my desktop simulator (http://aerowinx.com). Albeit this is a 744, but an incredibly accurate one in terms of aircraft and system performance simulation at that.

Using FLCH above FL300, with a heavy plane gave me a very long drawn out climb. So yes, it seems smoother, but on a 4000 ft step climb the last 1000ft took several minutes. I’ll try some more, I would think it would be better at lower altitudes.

Flyboy747 is along the lines I understood from KLM. But then again, to my earlier point, this is one topic where there are various insights.

My understanding is that everybody (?) uses ICAO step climb definition and your FMC would be set up accordingly. (FMC PERF INIT page)

That would mean you would get 2000ft increments up to FL290 and 4000ft increments above FL290.

On a fully loaded 777 what would be your initial cruise altitude? I would think it would be around FL290. (it is on a 744). So most of your step climbs would be 4000ft increments or not?

I suppose at least in theory 2000ft steps would be better from a fuel efficiency point of view. Maybe at some point in time we will get continuous slow ascent to get the most effective fuel burn. But that would require a major overhaul of the current ways of assigning ‘fixed altitudes’.

I believe the only plane that did a “continuous step climb” was Concorde. But then they were flying way above everybody else.

Just sharing: I’ll be piloting Concorde in a few months. Well, at least, I’ll be flying left hand seat on the original BA Concorde simulator at Brooklands Museum, UK.

http://www.brooklandsconcorde.co.uk

Just booked my trip in September! Can’t wait!

Jeroen

[searchingheaven]

Originally Posted by flyboy747

While that is true, in cruise for a step climb of even 2000 feet, which is mostly the case, we stay on VNAV.

Also, congratulations searchingheaven for an excellent review of the triple. Happy landings and tailwinds.

Of course it varies from carrier to carrier. At our carrier on the 777-300ER, we use FLCH whenever possible.

And thanks for the compliments. You rated for a 747?

[flyboy747]

Originally Posted by searchingheaven

Of course it varies from carrier to carrier. At our carrier on the 777-300ER, we use FLCH whenever possible.

And thanks for the compliments. You rated for a 747?

Yes I am, been on the fleet for the past 10 years. Love it.

[Gansan]

Originally Posted by searchingheaven

However, the aircraft I fly, has 140,000 kgs of fuel on some routes.

In general, fuel jettisoned above 5,000 to 6,000 feet will completely vaporize before reaching the ground.

Wow! How much will that be, converted to litres?

Also, tell us more about the fuel itself. I have read it is actually highly purified kerosene. Is that so? How much fuel will be consumed in an hour for the 777 in flight, under normal circumstances?

Can turbine engine aircraft use some other fuel too, such as HSD?

[searchingheaven]

Originally Posted by flyboy747

Yes I am, been on the fleet for the past 10 years. Love it.

Well, then you must be much more senior than me. I have spent just 3 years with the 777, and as a F/O.

Originally Posted by Gansan

Wow! How much will that be, converted to litres?
Also, tell us more about the fuel itself. I have read it is actually highly purified kerosene. Is that so? How much fuel will be consumed in an hour for the 777 in flight, under normal circumstances?
Can turbine engine aircraft use some other fuel too, such as HSD?

In litres, it would be equivalent to 181,283 litres.

There are currently two main grades of turbine fuel in use in civil commercial aviation : Jet A-1 and Jet A, both are kerosene type fuels. There is another grade of jet fuel, Jet B which is a wide cut kerosene (a blend of gasoline and kerosene) but it is rarely used except in very cold climates.

JET A-1
Jet A-1 is a kerosene grade of fuel suitable for most turbine engined aircraft. It is produced to a stringent internationally agreed standard, has a flash point above 38°C (100°F) and a freeze point maximum of -47°C. It is widely available outside the U.S.A. Jet A-1 meets the requirements of British specification DEF STAN 91-91 and ASTM specification D1655 (Jet A-1) and IATA Guidance Material (Kerosine Type).

JET A
Jet A is a similar kerosene type of fuel, produced to an ASTM specification and normally only available in the U.S.A. It has the same flash point as Jet A-1 but a higher freeze point maximum (-40°C). It is supplied against the ASTM D1655 (Jet A) specification. The primary difference in the two types of fuel is the Freezing Point, Jet A freezing at a higher temperature than Jet A-1 and Jet A-1 has an anti-static additive. There is no measurable difference in the SG of types if they are both at the same temperature.

Fuel Burn rates

• Taxi Fuel Burn - GE Engines 2,000 kgs/Hour
• APU Fuel Burn - Ground consumption 240 kgs/hour - In-flight consumption 140-270 kgs/hour dependant on Altitude and Weight
• Cruise fuel consumption 8550 kg/hr during initial climb. Then it hovers around 8100 kg/hr for cruise phase. Descent rates are around 7750 kg/hr.

The variation in fuel burn rates of the 777-300ER is high due to the fact that we have around 100,000 kgs of fuel on 10 hr+ routes.

[airforce1]

Nice thread searchingheaven!

Also, I believe the longest passenger flight is flown by Boeing 777LR. Am not sure, if it is Delhi- San Francisco or the Dubai- Panama City...

[SPIKE ARRESTOR]

Originally Posted by searchingheaven

Feel free to challenge me, disagree with me, or tell me I’m completely nuts.

Hello Searchingheaven, thanks for sharing this lovely thread. As a kid I wanted to become a pilot, although I didn't get to fly machines in the skies, I manage to fly machines on the ground

Could you please tell me how is the V1 speed calculated, and any such important calculations you do before / during the flight ?

As a Pilot, what are your biggest fears (if any), I've seen a lot of air crash investigaton documentaries, so sometimes I've wet pants while I'm flying. I know the probability is too low though, but just want to know your thoughts on this.

Thanks !
Spike

[searchingheaven]

Originally Posted by airforce1

Also, I believe the longest passenger flight is flown by Boeing 777LR. Am not sure, if it is Delhi- San Francisco or the Dubai- Panama City...

Thank you for the compliments. The longest flight, in terms of distance, would be the Dubai-Auckland EK449, operated by Emirates. The inaugural flight was with a A380, but the 777-200LR will fly that route regularly. It says a lot about the market for four-engined aircrafts when 15 out of the top 20 longest flights are operated by a 777.

Originally Posted by Jeroen

My understanding is that everybody (?) uses ICAO step climb definition and your FMC would be set up accordingly. (FMC PERF INIT page). That would mean you would get 2000ft increments up to FL290 and 4000ft increments above FL290. On a fully loaded 777 what would be your initial cruise altitude? I would think it would be around FL290. (it is on a 744). So most of your step climbs would be 4000ft increments or not?

Jeroen

No, RVSM(Reduced Vertical Separation Minima) is now implemented almost in the whole world between FL290 and FL410. Under RVSM rules, the vertical separation between two aircrafts has been reduced to 1000 ft on opposite course on the same airway. Therefore, the next available level in your direction is 2000 ft. Above FL410, the vertical separation has to be a minimum of 2000 ft, for which the next available level will be 4000 ft.

The default step size in the 777 FMC is RVSM. But it accepts any of the following values:

• 0 : no step climb
• RVSM: steps every 2000ft
• ICAO: steps every 4000ft
• Manual entry (1000...): steps computed on the value entered.

We use RVSM step size to perform step climbs most of the time. 2000 ft step size is always more economical than 4000 ft. To perform a step climb with the 777, you have to set the new altitude on the MCP, wait for the indication "Now" and then press the Alt intervene button on the MCP. The AP will then switch to VNAV SPD and THR REF and climb to the new altitude.

Originally Posted by sriramr9

Few more questions from my end :
1. With so much automation is it still possible to fly the airplane manually by overriding auto pilot and shutting it off. Will it not give the pilots the real world experience to handle during crisis instead of synthetic feel?

2. Between joystick and yolk which is a more fool proof way of medium in terms of safety . I hear joystick handle independently does it not give birth to irrational inputs by both officers at same time ?

3' How does a aircraft successfully ground the residual voltage after a lightning strike despite no contact with earth?

4. In case of AF447 during violent descent did the deicing on pitot not happen?? In case of successful de icing of pitots theoretically the systems should resume back right as air speed will be available ??

1. Yes, of course it is possible. And most pilots prefer hand flying the aircraft during landing. But the rising levels of automation in the cockpit has raised a lot of questions regarding our abilities to hand fly the aircraft. And as a pilot, I am worried.

Consider this. I have flown the 777 for around 500 hrs in the last 5 months or so. Out of those 500, I have actually hand flown the aircraft only for about 30 hrs or less. The rest of the time, the computer was flying. So, yes the increasing reliance on automation is a growing concern among industry experts. Simulator exercises have shown that pilots who typically fly with automation can make errors when confronted with an unexpected event or transitioning to manual flying. Pilots these days have a lot of flight hours under their belt, but they are low quality, so to speak. A lot of what’s happening is hidden from view from the pilots. When the airplane starts doing something that is unexpected and the pilot says ‘Hey, what’s it doing now?’—and believe me that’s a very very standard comment in cockpits today.

2. . Both the yoke and the side-stick are safe, if operated with proper knowledge of their behavior. The operation of two side-sticks simultaneously is known as DUAL-INPUT. It's one of the first things taught to Airbus drivers. The laws regulating DUAL INPUT are as follows.

• Normal operation : Captain and First Officer inputs are algebraically summed. But the total output is limited to the maximum output that one side stick can produce.
• Each side-stick has a priority button. This button dis-engages the autopilot and provides full control to that side-stick.
• If the priority button is held pressed, the other side-stick inputs are ignored.
• If a pilot presses and HOLDS the button for more than 40 seconds, latches the priority condition to that stick. Meaning the other side-stick's inputs are ignored even if the priority button is released.
• In case the other pilot wants control of his side-stick, he presses the priority button on his deactivated sidestick. Then it's active again. Last pilot who depressed and holds take-over button has priority; other pilot's inputs ignored.

I may be wrong though since I have zero experience with Airbuses. This is what I know from fellow pilots. RVD and coolboy007 will confirm.

3. Typically, a lightning bolt will hit an extremity, such as a wing tip, or the nose, and the current will travel through the aeroplane’s metal shell before leaving from another point – the tail, for example. The hull of the plane forms a Faraday cage. A Faraday cage is a hollow shell made of conducting material. A strong electric field outside the cage will force the charge in the material of the cage to redistribute itself, but the interior space inside the cage remains uncharged.

4. AF447's crash was a very unfortunate event brought about a lot of attention to what I said about the first point. Let me explain the crash to you first.

When the pitot pressure probe on the outside of the plane iced over, the airspeed indications became unreliable. The computer could no longer tell how fast the plane was going, and the autopilot disengaged. The fly-by-wire system switched to alternate law. First off, the crew failed to realize that the FBW had switched to Alternate law, which does not provide stall protection. Second, the crew were disoriented and didn't realize that they were stalling until the last minutes.

I believe that the autopilot cannot engage automatically when the airspeed becomes reliable. Anyway, by that time, both the pilots had already pressed the priority button & dis-engaged the autopilot.

Originally Posted by SPIKE ARRESTOR

Could you please tell me how is the V1 speed calculated, and any such important calculations you do before / during the flight ? As a Pilot, what are your biggest fears (if any), I've seen a lot of air crash investigation documentaries, so sometimes I've wet pants while I'm flying. I know the probability is too low though, but just want to know your thoughts on this.

Thanks a lot for the compliments. V1, V2 and all other speeds are calculated by the FMC(Flight Management Computer) in the 777. Most of the other calculations are also done by the FMC. There are very few things left for us to actually do these days.

This is the take-off page of the FMC which calculates the various speeds. You enter the flaps setting(mostly 5 for 777), CG% and the FMC does the rest.


This is the completed page with the speeds calculated.


As for my worst fear, a serious inflight medical emergencies ranks the highest. Medical emergencies can present an immediate life and death situation and decisions. If you are only talking about technical difficulties, the list for me is probably as follows:

1. Probe Icing
2. Depressurization
3. Dual Engine Failure
4. Thunderstorms