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Guest ALT2024

744 FD bars: rotation and initial climb

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Guest ALT2024

Hi. I came across this: http://www.aerowinx.de/archive11.cgi/noframes/read/5460where someone says that the FD bars aren't to be trusted for the initial climb away from the runway, i.e. following the pitch bar immediately it rises above 8 degrees nose up could lead to a tailstrike. Is this right?My usual technique is to rotate at Vr to the pitch director bar, then hold 8 degrees nose up, and then follow the FD bar when it rises further. This usually results in a climb speed of approx V2+15. At high gross weight I find I'm waiting a long time for the altimeter tape and rate-of-climb indicator to move, and by the time they do move noticeably, the FD bar has already risen and my speed is increasing.So, am I risking a scraped rear by following the bar, and should I be flying on the altimeter tape and rate-of-climb indicator instead?Rob

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Guest D17S

Just to venture a suggestion . . . 1) Maintain your initial rotation pitch by watching the little airplane against the degree lines on the ADI.2) Watch RA and VSI for conformation of lift-off.3) Smoothly, continue to rotate to maintain V2+10 or to stop the acceleration if beyond V2+10. Fly the speed tape. That's your real flight director. Why? This is just what the FD is trying to get you to do anyway, so . . . turn that dumb flight director off for all of this! That little FD switch on the dash? Click it DOWN. Once you can fly like this without the FD, it might be safe to turn it back on. For rotaton and a speed-on-pitch climb (especially!), the FD should always be source #2. This way you'll know when the FD is giving you bogas info and you can just ignore it. You're the boss here. Don't let all that fancy technology ruin your day.

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At rotation, pilots should rotate at a certain rate (3 degrees per second). Tailstrike will occur at 11 degrees, so you don't want to reach 11 degrees with the aircraft still on the ground. In gusty conditions, it's advised to delay rotation.During initial climb, the pilots use the FD as a rough guide.. As one person told me, they "look through" the FD (whatever that means :( ). As Sam says, the airspeed tape is the thing you have to watch.Cheers.Q>

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Pitch up at 3 degrees per second to an inital attitude of 15 degrees, the pitch command on the flight director isn`t actually doing anything untill VNAV engages at 400ft agl anyway!The important thing to watch is rotation rate and pitch angle,don`t worry about the speed,that`ll take care of itself,start trying to chase the speed during rotation and there`ll be a tail strike,though the speed you end up at will show it you over or under rotatedAfter Vnav engages the flight directors will jump to maintain your present speed if its between V2+10-V2+25.All the above technique is subject to software fit,not sure how the PMDG models it, but there is updated software that will give you initial pitch commands before VNAV engages.CheersJon

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"the pitch command on the flight director isn`t actually doing anything untill VNAV engages at 400ft agl anyway!"Depends on which trainer/training manual you believe ;) I've been taught that the A/P is able to control speed (to V2+10~25) after liftoff in TO mode without VNAV being armed. A Rockwell Collins A/P engineer just happens to agree with me on this, so you won't persuade me otherwise so easily.Rgds/Q>

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Certainly with the updated service software(should be on every 400 by now) the FDs will give initail speed control after lift off untill VNAV egages at 400ft agl, however this wasn`t always the case,and I`m not sure what PMDG have modeled.Either way the correct technique is to rotate at the correct VR at 3 degrees/second up to 15degrees pitch on the PFD,ignoring anything the FDs say(unless in a windshere escape mode) and hold it untill clear of the ground- (I use RA passing 50), the AP cant be engaged below 250 agl,and VNAV will kick in at 400agl so you`re only talking about a few seconds anyway.regardsJon

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Guest D17S

In TOGA pitch mode, prior to Vnav engagement, The AFS will command: 1)FMC's V22)lift off speed3 or an averaged speed after lift offwhich ever is greater. At Vnav engagement, the AFS will command:1) FMC's V2+10 knots2 or the current airspeedwhichever is higher.At acceleration altitude . . . away we go!

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"the AP cant be engaged below 250 agl,and VNAV will kick in at 400agl so you`re only talking about a few seconds anyway."Thanks, Jon.I understand about the limited time frame, but I'm wondering if TO speed guidance is completely disabled with inoperative FMC's. The 250' agl I may have heard mentioned before, but, frustratingly, I've never seen it written in a maintenance manual. It seems odd that you can engage (some) pitch modes on the ground, but not 1'~249' above it :(Cheers.Q>

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Guest ALT2024

Thanks for all the replies. This first few seconds of flight is obviously a hot issue.So this is my understanding of what I should do:Rotate at Vr, at 3 degrees per second.As the aircraft reaches 8 degrees nose up she should lift off. I can verify that this has happened by watching the RA and the VSI.Continue rotation to arrest the increase in IAS, and climb at constant IAS until acceleration altitude.Just to confirm: on a good day, if I get this exactly right, can I expect that I will be able to rotate smoothly all the way to 15 degrees nose up, at 3 degrees per second, and that lift-off will occur at 8 degrees without having to hold that angle and wait? (I understand, of course, that I should always check the RA and VSI before assuming the tail is safe, but could continuous uninterrupted rotation actually happen?)Sorry if I'm a little slow on the uptake :)Rob

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Rob,Yep, the most important thing is rotation rate, 5 seconds to get to 15 degrees, too quick and you`ll have a tail strike, too slow and you`ll use more runway. Its one of those basic pitch/power/speed couplings so 15 degrees at take off power will always give you the correct speed with TO power, give or take a knot or two.we are taught always to pitch for 15 degrees and hold till VNAV,the FD bars will come up to meet your pitch after rotation provided your speed is within the range V2+10to+25but,as Q says we tend to "look through them" till VNAV.Q,that 250 ft agl thing is in our ops manual part 1 limitations section if you have an equivalent? not seen it in the MEL or anywhere else.Its got to be,I would have thought an aircraft rather than company limit,as companies are very carefull about setting such limits for a legal point of view.CheersJon

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The 8 degrees pitch on the FD ADI is just arbitary. It only serves as a check during the preflight procedure. You would have to work really hard to scrape the tail on a normal TO.On a flap 20 TO the lift off attitude is 10 degress and the tail strike pitch attitude would be 12.5 degrees. As has been mentioned 3 degress (2.5 to 3) per second is the rotation rate you are looking for. This should take about 3 to 5 seconds to reach pitch target. A slow rotation rate will increase TO distance as would rotating to less than the correct pitch target. The Boeing flight manual says that the FD pitch command is not used for rotation. I would not advocate using 10 degrees as the standard pitch target. 15 degrees works fine in most cases (and is the figure to aim for in a GA around), however this can a bit on the high side for heavy weight TO's or large thrust derated TO's even though it is standard Boeing procedure. The procedure we use is to rotate to the 3 eng pitch attitude for the TOW. For a derated TO we reduce this by 1 degree. This seems to work out well as an initial pitch figure to aim for and it can then be fine tuned once the FD has a good target pitch sorted. It puts the aircraft in a good position should an eng fail after V1. A slight excess of speed on 4 engs is not a problem. As Sam has pointed out keep a good eye on the FD. I would not suggest that you turn the FD off. Would you kick start a motorbike that has electric start? The FD is an aid and should be used but like most things it should not be solely relied upon and at the expense of a good scan. At times you will need to "look through it". At lift off the FMC will update the target airspeed to the current airspeed as long as it is within the target of V2 + 10 to V2 + 25 until VNAV engages at 400 ft AGL.http://forums.avsim.net/user_files/162085.jpgCheersSteve


Cheers

Steve Hall

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"At lift off the FMC will update the target airspeed to the current airspeed as long as it is within the target of V2 + 10 to V2 + 25 until VNAV engages at 400 ft AGL."Personally, I don't think the FMC is a part of the equation for liftoff to 400', but since no airline pilots take off without the FMC being programmed, it's not something easily tested (and even when tested, it will be open to interpretation because of the variables involved).My training notes DO state that the A/P controls this period, so until I get something new from Rockwell stating otherwise, that's the opinion I will be holding :)Cheers.Q>

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My books are not as detailed as I would like but it does say " During take off the FMC updates the target airspeed to the current airspeed until VNAV activates.........". Something must be doing the calculation. If not the FMC then what can be?CheersSteve


Cheers

Steve Hall

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Guest D17S

Yea, I agree. The FD should be left on. We need all the resources we can get. But this being a video game and all, this totally cool (dude) resource does allow some unique learning/training opportunities. If a fledgling pilot wants to get a better feel for what is really going on during the 1st/2nd segment climb sequence, forcing the student to fly from the FD's source (raw data) might be helpful. I really like the anaolgy of looking through the FD. Maybe we just come up with a Flight Director Transparency Adjustment Controller (ahh, that would be a FDTAC!)Another great tool our sim allows is that slow-down control. I don't know how many TO's I've made at 1/2 speed. The roll takes a while, but that initial pre-Vnav engage climb just goes by too fast. 1/2 speed is the ONLY way to really get a grip on what is going on . . . but if you want to try this, get the airplane HEAVY. That's the only way you will be able to rein this rocket ship in to 'just' V2 for climb. Test flight: Set Acceleration Alt and THR Reduction for 9999. Engage the AP as soon as it will (50ft). Raise the gear. Don't touch the flaps. Just let the airplane hang there at what ever speed is flight directed. The AP will do exactly what the FD is telling it. This is really the only way you can see -exactly- what the FD is commanding. Do it with Vnav armed, then disarmed. Watch at 1/2 speed. Take notes. That TOGA sequence I described in the post above what I see in the PMDG model. This is what I looked for (and saw) in the Level-D 744 big-sim. I never was able to stay at V2, but the FD commanded my stabilized climb at about the FMC's V2+ 05 to 15 (depending on my rotational skill!) This was well below the MCP's (intentionally set) 250 knots -- and any flap limit, BTW. The FD was looking at something and it wasn't the MCP. We have a computer based trainer for Pegasus equipped 767/757's in the crew lounge. I get the same FMC /MCP functionality as with the 744 We really can't ask a revenue flight to mess around with this, but it seems really important information to know. For instance, if I revert to FLCH SPD during the 1st segment, I want that speed bug to hop well away from a typical V2+10 initial climb speed. I really need the detailed knowlwdge that the speed bug will go the MCP's setting +10 if something bad happens in the initial climb (i.e., an excessive pitch rate change or smacking the rake) That's why I want the MCP set to V2+10 tp begin with. I'll likely be at V2+10 for my initial climb and the speed bug (I'm focused on) will "hop" another 10 knots, demanding another 10 knot speed increase. If I had the MCP set to just V2, the bug would just hop to my current airspeed.Actually, it's just an interesting technical discussion about what drives the FD's command bar. IF I was going to be engaging the AP at 50 feet, that'd be another story. Here's why: With the AP engaged, where ever the FD goeth, so goeth the airplane. But in RL (I assume! _ not being a real pilot and all!) it's likely that the AP will not be engaged at 50 feet and primary flight direction will come from the speed tape anyway, so who cares? (having turned down the FDTAC so I can look right through those pesky FD command bars!) But on the other hand, it just seems to me these little details are really important.

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"If not the FMC then what can be?"If you compare TO with Go Around mode, you will see that the modes are very similar. First a minimum vertical speed has to be achieved, then the target becomes a mix of V/S and airspeed and if a second (higher) target V/S value is achieved, the pitch target becomes purely airspeed. AFAIK, the FMC has nothing to do with GA pitch mode (to have it dependent on the FMC would be preposterous). For me, it's not difficult to imagine the FCC's having the capability to guide the aircraft in TO mode.During take off the FMC updates the target airspeed to the current airspeed until VNAV activates.........". My interpretation of this is that the FMC is tracking the current airspeed target (as generated by the FCC's) until 400' when it takes over speed control from the FCC's. An analogy would be A/P "arm" mode... In arm, the A/P servos track the flight controls until you hit the CMD button (so there is no sudden changeover).Anyway, this is only one man's interpretation of what is written in manuals ;)Cheers.Q>

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