737NG LED's and speed limitations/ops

[galdian]

Hi all

Apologies if already covered, any references appreciated as know "the idea" but can't find more extensive explanations.

T/O in VNAV mode
Above acceleration altitude VNAV will set 230kt until all flaps (more importantly all LED's) are retracted as the LED's (apparently) have a limitation of 235 kts.
Reference??
Asking as ONLY limitation generally used is 250kts when flaps out (1, 2, 5 degrees)...full stop!

APP in MCP mode
Accept (and use) Boeing procedure as "set flaps up speed, approaching same select flaps 1..." etc etc however IN THEORY there appears no restriction in selecting flaps 1, 2 or 5 at 250kts and maintaining that same 250kts??
Any further flap selection of course at a speed of 210kts or less.

Asking as a F/O with flaps out after T/O selected SPD INT and set 240kts (scared of 250 below 10,000' which in Japan creates a paranoia so severe that it virtually requires the changing of flight deck seat covers a couple of times a day to remove the brown skidmarks!), I suggested 230kts initially and all OK.
Later when I tried to explain I couldn't - at least referring to the "simplistic" limitations we are provided where it is just "250kts EOFS"!
I'm aware of the 230kts limitation for alt extension but that's a non-normal.

I know there's a reason why the "250kts" is not the full story...but I don't understand "why".
Any assistance appreciated.

Cheers
galdian :ok:

[RAT 5]

Above acceleration altitude VNAV will set 230kt until all flaps (more importantly all LED's) are retracted as the LED's (apparently) have a limitation of 235 kts.

Will it? I've never made a VNAV takeoff, so can not confirm. I thought the most common method was to BUG UP at acceleration altitude and then select VNAV when flaps are up & clean. To use VNAV on takeoff, as we did in B767, would perhaps require a V2+20 speed restriction unto acceleration altitude. In VNAV, once passing this altitude, the speed bug would increase. Is this the procedure you are referring to?
Why, on takeoff, would you want to select 240kts BEFORE clean. On even the shortest flight how many seconds is that going to save, if any? So why do it? Not good airmanship.

The 235kts is for LED's at FULL EXT & is used at the beginning of ALT EXT as you say.

On APP why would you select through to F5 and maintain 250kts? The only reason could be to increase ROC. That's what SPD BKS are for. The FCTM says Flaps should NOT be used as speed brakes, but I suspect that is more for the slowing down scenario. F5, SPD BK 210kts is a great 'get you down quick' configuration if held high and nearing the approach route.
Another safety reason for not maintaining high speed with LED's out is system stress. Limitations are not there to be used as the norm', (except if they are FTL's and minimum fuel.) Plus, what happens if there is an LED malfunction, or you mis-select F10 and the LED's go to FULL EXT at 250kts. You might lose an LED and end up in an UA.
If you are selecting flap on app then you are getting closer to the runway and you need to slow down, hence the flaps; so why fly high speed with lift & drag? Not good airmanship.

This desire to fly high speed is questionable. You program VNAV PTH to achieve an energy profile from TOD to OM. It usually includes a 250/FL100 transition. I used to fly with so many guns-ho macho wiz-kids who asked for high speed below FL100. ATC said OK. Later o the were pulling SPD BK's. Go figure. Not good airmanship. Same guys drive high speed towards red traffic lights and roundabouts. Not good chairmanship.

[Denti]

VNAV takeoff (armed on the ground, active at) is the standard boeing SOP since FMC 8.1. And yes, it does command 230kias until the LEDs are retracted. From what i heard is the 20kts buffer simply a safety buffer to the 250kias limit for sloppy flying. Especially if the autopilot is already active and the plane encounters a windshear the ability of the autopilot to recover would not be sufficient if VNAV commands 250kias.

[Avenger]

VNAV will command 230 KTS until flap retraction in accordance with the skew protection speeds advised to prevent roll if the devices are asymmetrical. On take off we generally high increasing energy and higher angles of attack, on approach, energy is decreasing and lower angles of attack. It just makes for good airmanship.

[galdian]

Thanks all for replies, however maybe some misunderstandings.

All have offered OPERATIONAL thoughts, I'm asking if anyone can advise WHERE:
- the alleged 235 kts limit because of LED's can be sourced;
- why, in simple terms it appears there's a "phantom" 235kt limitation on departure but, in theory, 250 kts for flap extensions 1,2,5 on approach are OK.

RAT 5

Thanks, but your first statement is that you "don't use VNAV" and bug up manually.
That's fine - but my question was related to VNAV which for myself has been SOP on the NG for the last 10 years.
My question regards APP (approach) well read again please, I follow the FCTM but the question was, IN THEORY you could select flaps at 250kts.

I am not asking about personal operational philosophy - just asking why there appears "hidden" speed limitations which (apparently) also vary whether on T/O or on APP.

If anyone can assist appreciated - just one of those "bugging me" things.
Cheers
galdian :ok:

[Skyjob]

VNAV takeoff (armed on the ground, active at) is the standard boeing SOP since FMC 8.1.

Not entirely standard, as there is an active bulletin on the matter which some airlines take to heart in not allowing crews to use the mode as advertised until a fix has been provided:

Subject: Impact of Arming VNAV on the Ground on the Windshear Escape Maneuver (FMC Update 10.8 and 10.8A)
Reason: This bulletin informs 737NG flight crews of the need to revise the windshear escape maneuver if VNAV has been armed on the ground for takeoff (FMC Update 10.8 and 10.8A).

Background Information
During airline simulator evaluations of FMC Update 10.8A, an unintended consequence of arming VNAV for takeoff was discovered with respect to the windshear escape maneuver. If VNAV is armed on the ground, it will remain armed even if TO/GA is pressed below 400 feet AFE in accordance with the windshear escape maneuver. At 400 feet AFE, VNAV will engage and windshear guidance will be lost. TO/GA must be pressed a second time when above 400 feet AFE in order to regain the appropriate windshear guidance.
This condition exists on FMC Update 10.7, 10.8 and 10.8A. Arming VNAV on the ground is not permitted prior to Update 10.8, however.
Boeing and GE are discussing a potential fix for this anomaly in a future FMC software update.

Operating Instructions
Arming VNAV on the ground is not permitted with FMC Update 10.7 or earlier.
With U10.8 or 10.8A installed, if unstable weather conditions are present prior to takeoff, consider not arming VNAV for takeoff.
If VNAV has been armed for takeoff and windshear is encountered, press either TO/GA switch and accomplish the Windshear Escape Maneuver. If windshear conditions continue above 400 feet AFE, press either TO/GA switch a second time when above 400 feet AFE. Verify TO/GA engagement and continue the Windshear Escape Maneuver.

[B737SFP]

Well, I'm not sure if this is the reason, but:

Let's say that during your departure, after commencing the flap retraction, you get a LE FLAP TRANSIT.

Let's read the Flight Controls - LE FLAP TRANSIT NNC, shall we ?

Guess what (9.12 - Step 6) !?!

Light(s) for more than one leading edge device
is illuminated:

Limit airspeed to 230 knots maximum.

I don't know but, probably, Boeing is just trying to help us don't fck things even further in case of a LE devices malfunction. Max speed will be there, don't touch nothing, read the checklist, voilá.

:ok:

[Derfred]

I've heard as many theories on the 230 kt VNAV bug as there are stars in the sky...

Rhetorical question... what is flaps up manoeuvring speed at MTOW?

[RAT 5]

Rhetorical question... what is flaps up manoeuvring speed at MTOW?

There is a multitude of MTOW (structural) depending on how much you paid for. At 75.0T it is 221kts on NG-800

[Denti]

Not entirely standard, as there is an active bulletin on the matter which some airlines take to heart in not allowing crews to use the mode as advertised until a fix has been provided:

Which is then a company SOP. In the bulletin you posted the base assumption is that VNAV take off is the standard and under certain conditions the pilots should consider to deviate from that standard. SOPs after all are only standard procedures, and pilots can, and often should, deviate from them.

[galdian]

Thanks all

Appears no one can assist with original question - is there anywhere where Mr Boeing explains why VNAV sets 230kts until all flaps/LED's are fully retracted YET on approach (in theory) you could set flaps 1,2 or 5 at - and maintain - 250kts.

Cheers
galdian :ok:

[B737SFP]

Just as a matter of curiosity...

Let's say that you guys are doing a normal takeoff with VNAV and LNAV engaged (FMC 10.8A+)... In case you have an engine failure, what your company SOP says ? Do you guys revert from Vnav to LVL CHG at the acceleration altitude, or do you guys fly VNAV even when single engine ?

My company says that we should request LVL CHG and set flaps up speed at the acceleration altitude, but, BOEING clearly says in the FCTM that when doing a VNAV TO, in case of an EO, VNAV will set FLAPS UP speed at the acceleration altitude...

So... I don't know if they missed that part, or if there's anything else that I'm not aware of.

:ugh:

[Avenger]

Galdian, if you are limiting your thinking process to VNAV constraints, VNAV will set the max speed for the alternate flap extension as 230 its due no skew or asymmetry protection. On approach in VNAV if you select flaps at 250kts the command speed will be the speed for the current flap section.. not 250 its. If you select flaps above placard speed the A/T lim amber light illuminates with msg " drag required" . Of course we can be num skulls and select flaps at any speed, but thats just poor airmanship, poor understanding of energy management and poor systems knowledge. Flaps are lift devices and not recommended as drag devices or to increase ROD (FCTM)

[Denti]

The FMC should recognize a OEI situation and then switch automatically into the OEI mode, using the OEI acceleration altitude and speeds. Therefore VNAV is not a bad situation if you fill in the take off page 2.

[Derfred]

There is a multitude of MTOW (structural) depending on how much you paid for. At 75.0T it is 221kts on NG-800

Yes, and at higher MTOW it gets closer to 230kts. Ours are 79.0T and it's 224kts. I'm just throwing in another theory that was suggested to me once upon a time... Plausible, but with no more authority than any other theory I've heard.

Some suggest that it's due to a LED limitation of 235kts. That is not published in my manuals. The LED limitation is obviously 250kts for flap settings up to 5 (and alternate flap extension is irrelevent to this discussion).

However, up to flaps 5, the LEDs are not fully deployed. Boeing permits up to flaps 25 for take-off. In non-SFP variants, the LEDs are fully deployed at take-off with flaps 15 or 25.

So, is there indeed a secret 235kt limitation on fully deployed LEDs?

During a VNAV flaps 25 take-off, does it still bug 230kts? If so, it might be protecting the LEDs, but it ain't protecting the trailing edge flaps. (I'm asking because I don't know. I haven't ever tried greater than flaps 5 for VNAV take-off.)

Another question is: why a hard 230kt figure in the first place? Lazy programming? VNAV knows the flaps up manouevring speed for the aircraft weight, so why doesn't it just bug that? After all, that is what gets bugged via the MCP when flying non-VNAV departures.

[Jwscud]

The QRH LE FLAPS TRANSIT NNC asks you to limit your speed to 230kts if more than one LED is extended and TE flaps are retracted.

It is also the limit for use of Alternate Flaps.

235kts is the gear retract limit speed but nothing to do with flaps.

[Derfred]

The QRH LE FLAPS TRANSIT NNC asks you to limit your speed to 230kts if more than one LED is extended and TE flaps are retracted.


And that is relevant how, exactly?

[framer]

I see the relevance. I have never had it happen apart from in the sim but if I am cleaning up and I get the leading edge flap transit light, the first thing I plan on doing after establishing who is flying the aircraft and that terrain isn't a concern is selecting v/s 1500 and 220knots and asking for the checklist. The vnav function of limiting to 230 will have kept me within limits until that point.
Fair?

[Skyjob]

is there anywhere where Mr Boeing explains why VNAV sets 230kts until all flaps/LED's are fully retracted YET on approach (in theory) you could set flaps 1,2 or 5 at - and maintain - 250kts.


It has to do with the limitation of LED when fully deployed.
On most takeoffs (using Flap 1 or 5) and when selecting 1-5 on approach the are partially extended and have a 250kts limitation. Fully extended the limit is reduced.

VNAV helps pilots in many ways, as described by others above, like in OEI operations provided Takeoff page 2/2 is entered with relevant data (acceleration altitude for NADP 1 or 2, OEI retraction altitude etc), or 240kts below FL100 in descend to allow buffer not to exceed 250kts (many of out company pilots seem to believe this is due to a FMC coding error, or requirements in USA, but this is not the case (ref: Boeing Supplementary FMC Documents regarding VNAV algorithms)), it prevents overspeed in both Mach and KIAS flying range, equally will not allow exceeding 230kts when LEDs are extended during flap retraction.

The guys and gals that wrote the software for VNAV are very bright and not all their decisions are described in our manuals. But lets just summarise it in the fact that VNAV under no known condition will (autonomously) take the aircraft outside its protected range, or else it would not be certified by FAA without limitations.

And framer: yes VNAV would have kept you safe, no need for LVL CHG or V/S

[galdian]

Skyjob
OK hopefully the last question:


- on descent NOT in Vnav but MCP mode we can - in theory - set flaps 1, 2 or 5 at 250kts and maintain 250kts.


There is no limitation or mention made by Boeing in this case.


On takeoff in either Vnav or manually setting green dot we have 230kt protection - understood.
On descent in MCP we - in theory, as above - do NOT have any note or limitation.


Why are the LED's so important on takeoff but - potentially, in theory - not on approach??


I am well aware of recommended not to use flaps as speedbrakes/the alternate flap extension of 230kts etc etc which are side issues to the question.
Cheers!

[Skyjob]

Why are the LED's so important on takeoff but - potentially, in theory - not on approach?

The LEDs are important in both scenarios.
However the takeoff with flaps greater then 5 selected allows departures with full extended LEDs.
Retraction failures are possible, mechanical problems or an environmental "impact" could result in a situation where one or more LEDs may not retract to partial, subsequently preventing a complete retraction, something which can be verified on the overhead indicators in LE stay in transit.
On departure, there is thus a risk that there could be one or more fully extended LEDs which you wil not find out about until retracting flaps up as I am sure you will not look during flap retraction on departure at the overhead panel to confirm partial retraction has been achieved...
Thus to prevent an inadvertent acceleration beyond 230kts with the potential that a fully extended LED is present, Boeing decided to prevent VNAV from accelerating above 230kts until LE TRANSIT/EXTENDED lights are extinguished.

On approach, the logic is in reverse.
The LE are retracted and extend to partial with the initial fall selections. They will only be fully extended with selection of flap 10, thus below 210kts, again preventing full extended LED in flight at speeds above 230kts.

Hope this helps

[B737SFP]

Hmmm...

What about the SFPs ?

The slats only go full extended beyond flaps 25 !

And his VNAV system logic for departure is just the same of the other versions...

:confused:

[Derfred]

But lets just summarise it in the fact that VNAV under no known condition will (autonomously) take the aircraft outside its protected range, or else it would not be certified by FAA without limitations.

Wow, you've obviously never flown a B737 in VNAV. You're saying that leaving it in VNAV at 230kts, the aircraft will not exceed 230kts? Yet you also say it selects 240kts to provide a margin for 250kt speed limit below 10000'.

So, again I ask, why 230kts? Why not flap-up manoeuvring speed? At least that would be consistent with a non-VNAV take-off, and would actually do more to prevent 230kt overspeed in this LE flap transit event that everyone is panicking about.

[galdian]

HI everybody for taking the time to reply, I think in particular Skyjob may have hit the (final) nail on the head.

Amazing how quickly you forget - in previous companies on classics there were flap options (1,5,15) for T/O so the potential to T/O with LED fully extended....although F15 was very infrequently used.
In present company on NG only F5 is used at all times.

So either a VNAV or a manual green dot retraction will provide "protection".

On approach VNAV will set the appropriate speed for any flap selected, in MCP operation full LED extended will not occur until flaps 10 selected (210kts max), if you don't bust the flap limitation speeds then approach also has "protection".

All makes sense, great stuff! :ok:

NOW the ONLY remaining point: IS THERE, actually, a structural/engineering limitation of 235kts with LEDs fully extended?????????
Or just a Boeing aviation urban myth!!!!!!!!!!:ooh:

If there IS there would be no need to worry the humble drivers - who already have enough to worry about as (as above) any such limitation would be covered.

Anybody who CAN quote, or better provide, anything from Mr Boeing??

Once again thanks all - greatly appreciated.

[Chesty Morgan]

Derfred, I thnk you need to understand what 'autonomously' and 'take' mean.

[shlittlenellie]

Skyboy is correct.

Another poster wondered about VNAV exceeding the flap limitation for a flap 25 takeoff. VNAV commands flap placard -5 knots for take off (so for flap 25 and above acceleration altitude, VNAV commands 185 kts).

Another question was about engine failures and VNAV, the FMC does detect the engine out condition and VNAV commands Vref40+70 above the Engine Out Acceleration Altitude set in Take Off page 2. If there's an emergency turn then SPD INTV is used to prevent the acceleration. The other bonus of 10.8 and VNAV takeoffs is that the autopilot is available with a single engine on takeoff above minimum engagement height (400'). It works well and changes the habits of a lifetime on a 737.

As for the 230 kts limitation... It's not in the limitations since it applies to a non-normal condition. Hence, it's in the QRH, as mentioned, for a LE flap transit light illuminated with trailing edge flaps up, i.e. leading edge device fails to retract. VNAV's acceleration speed logic, makes logical sense: flap placard limit -5 and leading edge failing to retract protection. The leading edge flaps will always be fully extended and the leading edge slats will be partially or fully extended depending on the flavour of 737 for every takeoff. So the system is programmed to ensure that the leading edge devices are fully retracted before commanding an acceleration above 230kts. Watch the LED lights on the overhead panel and ask your colleague when the VNAV command bug moves from 230 to 250 kts.

Outwith VNAV, what you do with the MCP SPD window is what's limited by your fingers and your head. Before VNAV on takeoff and 10.8 logic, VNAV wasn't selected after takeoff until the TE flaps and LEDs were fully retracted for LE speed protection and UP speed was never more than 230 kts for even the heaviest variant, hence VNAV continues to demonstrates LED speed protection.

In respect of the approach, aiming or having to extend flaps at the limit speed points to a mis-managed approach. The limit speeds are limits, not targets, as previously stated. Extending flaps as the appropriate manoeuvering speed is approached is better practice and demonstrates better planning ahead - rather than the descent and approach anxiety commonly seen in some less experienced pilots.

As asked before, why would you set 240 kts before the flaps were retracted? What does it gain and aren't you contravening SOPs as well as the Boeing's directions in the FCTM? They designed it.

Mentioned previously: 240kts in FMC below FL100 is only pre-programmed for descent and it has 250/FL100 for climb on the 737. Look at instrument approach design criteria in ICAO 8168. The range of speeds for initial approach is 160-240kts for a CAT C aircraft. Cat D is 185-250. If a Boeing Cat D aircraft FMC also has 240/FL100 in the descent page then logically it's a buffer for the speed limit. Why is that "buffer" not applied in the climb? It's been a while and I can't recall for Cat D. Add to this that most Boeing Cat D aircraft using the MTOW logic for flaps up manoeuvering speed will have a speed of more than 250 kts when clean after takeoff. If that logic isn't used for Cat D then at most long-haul weights, the actual clean speed will still be >250.

Structural limit for -800 fully extended leading edge devices? The TE limit would apply and so the relevant limit would be the F30 limiting speed (175kts) for SFP and Flap 10 (210kts) for non SFP. For the purist, with no trailing edge flaps and fully extended leading edge devices, it would be another non-normal condition and the QRH for Trailing Edge Flaps Up Landing has a 230 kts maximum when the alternate flaps system is used to extend the leading edges.

[Avenger]

Extract from Systems manual:

Normally, the target speed is economy speed above the airspeed restriction altitude and 240 knots below that altitude, until deceleration for approach. VNAV will not permit descent below the airspeed restriction altitude until the airspeed is at or below the restricted value plus ten knots. The start and end of the airport speed restriction deceleration segment is shown on the map as a green open circles with no labels.

Some people are are adjusting this speed in the DES PATH page to 250 its, in which case the monitoring will be 250-260 its.. not recommend!

If the aircraft cannot decelerate it will fly level until the speed is achieved and the path will slide down.

The "structural limit" for ONE leading edge device extended is 300 its, but Boeing allow for the worse case of multiple devices and thus limit to 230 kts. The limit is not prescribed by the trailing edge devices as if the alternate system is used to extend ONLY the trailing edge devices can be retracted and in the event of a go-around you would need to be above the trailing edge device speed with the LEDs still extended.

[framer]

And framer: yes VNAV would have kept you safe, no need for LVL CHG or V/S
Yeah I know, I just have a weird thing about blasting up with full thrust and low speeds, it's just so I can take a bit of puff out of the engines with the automatics still in. I wouldn't use level change, and only v/s after having a think about whether it is appropriate at that time.

[Skyjob]

Wow, you've obviously never flown a B737 in VNAV. You're saying that leaving it in VNAV at 230kts, the aircraft will not exceed 230kts? Yet you also say it selects 240kts to provide a margin for 250kt speed limit below 10000'.

Alas too many hours I have, my friend...

"**** in, **** out" comes to mind when you refer to VANV not maintaining 230kts in a DESC, as VNAV can only be as good as the data you put in the forecast pages for it to calculate a CDA. Incorrect winds are the most common problem when experiencing this, every second FO does that when starting on the line, not realising... An accurate forecast model allows for an accurate CDA with the VANV PTH speed as defined by CI.

In climbout, VNAV PTH acts similar to LVL CHG and pitches for the FMC commanded speed, that speed being defined by a virtual point 180nm after takeoff, based on the track direction at this position, the wind direction and speed as per TOC WIND, FL entered, ISA Dev and CI.

[Avenger]

In climbout, VNAV PTH acts similar to LVL CHG and pitches for the FMC commanded speed, that speed being defined by a virtual point 180nm after takeoff, based on the track direction at this position, the wind direction and speed as per TOC WIND, FL entered, ISA Dev and CI.
19th Nov 2015 13:04

Nope... VNAV speeds are determined by the restrictions in the legs pages and the climb profile. The pitch is related to power to respect those speeds at the thrust selected. VNAV makes 3 basic calculations based on the initial inputs to the FMC. up to 5000 ( terminal area) 5000-10000 (speed limited) above 15000 when VNAV will transit the thrust to full CLB if a reduction has been inserted at take off. The TOC and ISA deviation is used by the FMC to calculate the OPT/ MAX CRZ and M No. Virtual points 180NM? what happens on a 100 mile flight?

Agreed if you don't put in the forecast winds in the DES FORECAST page or forget engine anti-ice ON/OFF, to allow for increase in N1, the path is not calculated correctly and VNAV will not retain the DES SPD as shown with Msg " drag required" in scratch pad. If VNAV cannot manage the path then VNAV SPD will appear in FMA and possibly " unable next altitude" in scratch pad. A quick look at LEGS route DATA will help you to see the times predicted at each waypoint. Its not rocket science to figure if the aircraft can loose 100 its and 10000 feet in 2mins.. well it is to some;(

CLB PAGE:

The page title displays the type of climb. Normally, the title displays ECON for the economy
climb mode. Fixed speed climbs modify the title.
XXX LIM CLB indicates the limit speed, XXX, is based on leading or trailing edge flaps:
• target speed is 5 knots below trailing edge flap placard speed
• speed is limited to 230 kts if leading edge devices are not completely retracted
ECON indicates the speed is based on a cost index.
MAX RATE indicates the speed is based on the maximum altitude over the shortest period of time.
MAX ANGLE indicates the speed is based on the maximum altitude over the shortest horizontal distance.


Flight Management, Navigation Chapter : 12-11 FMC Takeoff and Climb Section : 41
Fixed climb speeds display XXXKT for a fixed CAS climb speed or M.XXX for a fixed Mach climb speed profile. Reasons for fixed speeds are:
• takeoff/climb acceleration segment constraints
• waypoint speed constraints
• an altitude constraint associated with a speed constraint
• a speed restriction
• a crew entered speed.
Displays ACT when the climb phase is active.

[Chesty Morgan]

Why does climb speed vary with cruise wind then?

[Skyjob]

Chesty Morgan, quotes from FMC Supplemantary Data Document explain this as well as the 240/FL100 in descent:

The FMC defaults to the economy speed modes for VNAV operation. In addition, by default, a transition climb speed limit is observed below the speed transition altitude during climb (250 knots below 10,000 feet in the USA), and a similar limit, but 10 knots less, during descent (240 knots below 10,000 feet in the USA). The 10 knot margin was added to reduce the probability of exceeding the transition speed limit in turbulence. The FMC increases the transition climb speed at heavier gross weights to equal the flaps-up full maneuvering speed of VREF40 + 70 knots (minimum transition climb speed).

FMC generates CAS/Mach speed schedule based on a fixed speed throughout the climb, as a function of cost index and initial climb weight. The speeds are calculated using a reference point 180nm downpath of origin, at which point the TOC wind component and predicted OAT are used to make corrections to the fixed speed. CAS is increased up to 40kts with 150kts headwind, decreased up to -20kts with 150kts tailwind, increased up to 4kts with ISA -40C and decreased up to -30kts with ISA +40C [no effect between ISA 0C to +10C]. Econ CLB Mach is set equal to ECON CRZ at the estimated initial cruise conditions. Thus to derive the Econ CLB Mach, estimate TOC Weight, Altitude, Wind and Cost Index are required. PERF INIT provides input area for all calculations.

Avenger, please provide references to your quotes regarding "VNAV makes 3 basic calculations based on the initial inputs to the FMC. up to 5000 ( terminal area) 5000-10000 (speed limited) above 15000", its areas of applicability, etc.

We all know a speed restriction in VNAV CLM is limiting acceleration, thus my post stating VNAV CLM acts as LVL CHG did not refer to this, merely to full climb scenario. In fact such speed limits are not adhered to as minimum speeds based on Flap position are observed by VNAV, protecting you from flying too slow. On your next departure try entering 180kts at the third or so waypoint, engage VNAV and treract flaps, it will fly Flap Up speeds to your surprise.

Furthermore, I cannot find any references to VNAV modes or calcuations being different below 5000'.

The thrust reduction below 15,000' as well as 250/FL100 equally have nothing to do with VNAV as it is an autothrottle/FMC function, as such it is avaialble in ALL thrust modes with a closed IAS window, not just VNAV CLM.

[Chesty Morgan]

Skyjob, thanks but it was rhetorical. :ok:

[galdian]

Hi all

Just to finish off my original question - info from the maintenance dept shows that 230kts is the point after which (if leading edge devices are fully extended) inspection(s) by maintenance are required so obviously comes down to a load limit/airworthiness question.

Phase 1 or 2 inspection (or a mix) depends on speed over 230kts - but that's another thing altogether.

Thanks for playing! :ok:

Cheers
galdian