Takeoff...Always blowing through VNAV max speed

[Guest sgfintl]

I'm having a heck of a time keeping the queen from just exploding through my speed restriction on take off. I set VNAV to 250/10000; ensure that on the legs page the initial segments between ground and 10,000 are at or below 250. I think I'm doing everything correctly--I'm pretty competent at the FMS and MCU. I use a derated TO thrust (45-54 degrees)...Another problem--especially if the bird's light--is keeping the FPM climb to something reasonable (3000fpm or less)... I'm sure that these two things (speed restriction and climb rate) are interrelated.My workaround is simply to use the autopilot functions without selecting VNAV. That way I can control both speed and climb--but I know this isn't the way it's supposed to work.Thoughts from the experts???Thanks,Steve

[markadeane 272]

The climbout angle is a little steeper than you might initially think from a visual reference point. Early on I found I was under-rotating the aircraft so it was climbing sluggishly and under those circumstances it'll bolt through your target airspeed in a matter of seconds. The trick is to have the Flight Directors on and V2 set in the MCP IAS window, get a smooth positive rotation going at VR and then at the same time transition your eyes from the outside view to the PFD and follow those bars! Keep the back pressure on until the aircraft's nose meets those bars, then relax the pressure and trim it out. If you relax the back pressure before you hit that desired climb angle you'll be well though 250knots in no time.

[michal 44]

Are you sure you are using all the derate available to you? You can "legally" derate up to 25% of the full thrust. You can even combine fixed derate with the assumed temperature derate. Also, make sure you select the appropriate climb-out derate too. Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

[crvm 0]

>I'm having a heck of a time keeping the queen from just>exploding through my speed restriction on take off. I set>VNAV to 250/10000; ensure that on the legs page the initial>segments between ground and 10,000 are at or below 250. I>think I'm doing everything correctly--I'm pretty competent at>the FMS and MCU. I use a derated TO thrust (45-54>degrees)...>>Another problem--especially if the bird's light--is keeping>the FPM climb to something reasonable (3000fpm or less)... >I'm sure that these two things (speed restriction and climb>rate) are interrelated.>>My workaround is simply to use the autopilot functions without>selecting VNAV. That way I can control both speed and>climb--but I know this isn't the way it's supposed to work.>>Thoughts from the experts???>>Thanks,>SteveV2+100 is mostly ALWAYS faster than 250 knots...[h4]Randy J. Smith[/h4]AMD 64 4000+|ASUS K8V DELUXE|SAPPHIRE ATI X800XT PE|MUNCHKIN 3200|80 gig SATA|DELL 1905FP 19" LCD|TRACKir PRO|PFC JEPPESEN MOONEY YOKE|CH PRO PEDALS|

[emvaos 13]

Dear Steve,Let me help with this issue by clearing out two myths :(a) 250 below 1000. No ATC cop will take you to jail if you do more than 250 below 10000 ft. Particularly in the case of a 747 where after "flaps up" VNAV will shoot to minimum VREF30+100 below 10000. If this value is less than 250 (below 10000) then great it will do 250. If this value is greater than 250 (as is the case for gross weights greater than 270 tons) then it will do VREF30+100. That's how the system works and how 747-400's fly. ATC knows that. (:( What is "reasonable" climb rate ? How and where is this defined ? Departure procedures usually note a "minimum" climb rate (in fact climb gradient) enough for the aircraft to clear ground obstacles, terrain etc. A 747 must be able to attain that minimum climb rate with TWO ENGINES OUT. Else legally the aircraft cannot take off for obvious safety reasons. The passenger only feels two things : vertical acceleration and cabin pressure rate of climb. Provided that the cabin rate of climb is below 500 fpm (even better 350 fpm) and the aircraft climbs at a **constant** vertical speed, the passenger feels no difference whether the aircraft is climbing at 1000 or 7000 fpm. And yes this aircraft at low weights (say 200 tons or 440 klbs) will storm through 3000 feet at 6700 feet per min and 14.1 deck angle. At 10000 feet at 5700 feet per minute and 11 degrees. Even at 250 tons (550 klbs) a 744 will do 5200 fpm at sea level and 4500 fpm through 10000 ft. VNAV SPD means adjust pitch to maintain given speed target with thrust at max defined limit (e.g. CLB or CLB-1 or CLB-2). Hence, vertical speed is a result NOT a requirement. Derated climbs are used when a "sufficient" (mark the word :)) climb rate can obtained at low altitudes (at a lower thrust limit) to reduce engine wear and tear.Hope this helps.Vangelis===================================== E. M. Vaos Precision Manuals Development Group www.precisionmanuals.com=====================================

[Guest D17S]

Steve, I hear ya. . .

[Guest D17S]

Spoke to an MD11 crew one time that said it can take 22+ degrees of deck angle to keep a light airplane 'slowed down' to V2+15 (that's the pre-acceleration altitude airspeed MD11 crews can use). It's very interesting to calculate what deck angle or rate number might end up occuring but as Vangelis was saying, these are not your targets. You are going to fix power, then control speed with pitch. Deck angle and rate are just the results. And about the flight director? I've heard that some crews still using mechanical instruments simply shut off the flight director during the initial TO phase. It's a distraction. Why? The FD pitch bar is using airspeed as its source anyway, so just use the FD's source directly and forgo the bouncing bar . . . Fly airspeed. The deck angle and rate of climb will be what they will be. Don't be afraid to get that nose up. Use the ADI to keep the wings level . . . and to make sure you're not about to plow into the rake!

[markadeane 272]

So is this (and other posts here) to say that the FD bars are not reliable for establishing your inital climbout airspeed? Or just that the use of FD bars vs. airspeed tape is a matter of preference?I have never had any real trouble with the FD bars as a means to set the aircraft into an initial climb speed. However if that's not the way it's done I'd like to know for my own sake!

[Guest D17S]

My feel is that once you get into a modern, video based cockpit, it's more a matter of personal taste. In PMDG's 744 here, the pitch bar is very accurate. With mechanical instruments, you really want to use the airspeed indicator just because of the nature of the mechanism. I had the paper "blue sky" peal off the ball of an ADI and hang up on the horizontal airplane symbol. The poor 'ol flight director bars would drag along between the ball's flopping paper and the horizontal airplane symbol. There's (arguably) less to go wrong in a clock kinda thing (the AS ind), and as I'll argue, it's the source for what we're discussing here.It's all about knowing why things are happening or "Thinking inside the box" (Randazzo). In the discussion here, the flight director's pitch bar is just telling you what airspeed it thinks you should be using. The question then becomes "What do you think?" By using the airspeed tape, you are forced to be aware and in direct control. The FD bars will never be anything more that a communication device for some other piece of info. Essentially, the FD is redundant. In some cases, you will have access to the source of its information. If the source is convenient, the argument here is to use the source as your primary indication and the FD as a redundant, verifying indication. For instance, this is especially critical during TO. I've had instances where the command bars were way up there. (Telling me "Woah there, hot rod. Slow down.") Without watching airspeed, I have dutifully pulled the nose up to the command bars, just to have them pass me on the down side saying "Ok, that's enough." And we dance like that for a while. I chase, they run. What I do now is to make a mental note of what airspeed I want to fly my initial,

[ronzie 21]

There is a comment by Mike Ray in his Boeing 700 book for simmers referring to PIO (Pilot Induced Oscillation). This is triggered by pilots over correcting for instrument indications by not taking into account the lag in instrument response. This results if not implemented in the slower instruments catching up and passing your original intended attitude. The trick is to use several instruments not subject to lag in addition to making smaller smooth corrections allowing slower instruments to catch up.This is the way it is in real world flying (used to do GA). A perfect example of a lagging instrument is the VSI indicator which trails observed more immediate changes in altitude and airspeed.Great post about anticipation and "thinking inside the box". I just thought I'd post the official name for this consequence.

[Guest neeraj.pendse]

I once heard in RW a Lufthansa 747-400 pilot ask for "280 knots to clean up" after takeoff from San Francisco. He was cleared to 6,000. (I was flying a Cessna Skyhawk) The ATC said it was OK. The plane was no doubt was indeed heavy, it was San Francisco -> Frankfurt.- Neeraj.

[Guest D17S]

I agree. That VSI really needs to be, pretty much, a non-player during a speed on pitch climb. But consider the other end. I use the VSI as an early warning system for glide slope deviation on approach. I'll get the glide slope 'dot-on' then fly the VSI. Generally I find that maintaining about a 700 FPM decent will keep right on the money (approach charts will have this number). I find that if I wait for the pitch bar to move, it's too late. I find the VSI will 'budge' before the pitch command bar or the GS dot. During approach, I use the GS dots to get me there and the VSI to keep me there. The pitch bar, once again, becomes just an excellent visual redundancy.And I talked to an A-300 crew about climb airspeeds last week. They said that center 'just said no' to an acceleration above 250kts below 10000 ft one time. They said they had to leave 1 degree of flaps out until they were cleared to accelerate. Like you said, if you're heavy, 250kts just won't cut it if you're all cleaned up. The FMC really wants to survive this flight and will direct you a faster speed if you insist on a clean climb. Big brother is watching!

[Guest BodoM]

Hi,as you seem the author of the 744 FDE, did you notice that the 744 is pretty overpowered on take-offs?Make the test. I have no problems to lift off with 380 tons on a runway which is below 10,000 feet. I believe Japan Airlines would be very happy if the real 744 would perform this as then they finally could start services from EDDL to RJAA.Boeing would be very proud if their real 744 performed in the way you modeled it.___________________________Best RegardsCpt. Bodo M