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During takeoff, the Boeing 737 encounters a distinctive "dead band" phenomenon after the initial pitch reaches approximately 10 degrees. Essentially, a slight increase in back pressure is necessary around 4-5 seconds into the takeoff procedure or when reaching the 10 degrees pitch to sustain the rotation rate.

While this heightened back pressure demand within the “dead band” is quite noticeable during initial training on the 737, it progressively becomes ingrained and intuitive through experience, etching itself into muscle memory.

Rotate at a rate​ of 2.0 to​ 2.5 degrees per second. Beware of a “‭dead‬​ ‭band‬” ‭​‬ around 10 degrees, and maintain a co‭nstant rate of rotation towards 15 ​‬ degrees nose up to a​ p‭itch limit of 20 degrees.‬

Boeing Flight Crew Operations Manual (FCOM) - Takeoff Procedure

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Although the Flight Crew Operations Manual (FCOM) addresses the "dead band" effect during the takeoff procedure, as far as I am aware, it is not mentioned or discussed in the Flight Crew Training Manual (FCTM) or the Airplane Flight Manual (AFM).

Based on my understanding, this "dead band" effect during takeoff is attributed to the combination of downwash off the wings and ground effect phenomena, resulting in diminished elevator effectiveness. Is this explanation accurate?

Furthermore, does this dead band phenomenon occur to the same extent in other Boeing aircraft or similar narrow or wide-body commercial aircraft?

tedioustortoise
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    WIth T tails on some airplanes the problem is the opposite; you have to relax a little bit to keep the same pitch rate. In that case it's mostly the T tail moving deeper into the downwash field and the fact that the gear with tail mounted engines is farther aft to keep the thing from tipping back when empty. – John K Jun 13 '23 at 18:58
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    To your second question, it affects the 767 as well. To your point, primarily ground effect, it does impact other airframes but I think the 737 got so much press around it due to flight simulators emphasizing the effect relative to what some pilots felt the effect was on real aircraft. Most flight instruction curriculum lists it as tail going into ground effect, but the downwash also effects it. Pilots will tell it's noticeable on the 767 as well. – Benloper Jun 14 '23 at 11:52
  • It is noticeable on the real aircraft too. – tedioustortoise Jun 14 '23 at 12:23
  • It seems you already asked this question two years ago. Related discussion at PPRuNe. – mins Jun 23 '23 at 11:06
  • Interesting. Wasn’t me though – tedioustortoise Jun 24 '23 at 15:18
  • Even from your drawing you can see that the wings are aligned at the same height of the elevators. You have then turbulent flow reaching them, reducing their effectiveness (negative lift in this case). Ground effect will also augment the pressure of the lower part of elevators, which is not what you want in this case (lift should be downwards) – maximusboscus Sep 15 '23 at 12:13
  • Additionally, since the 737 is not fly-by-wire like "Scarebus" I would expect/imagine stick getting "softer" in that moment, similar to a stall. At least in a glider (from experience) we can feel it easily (we have a big window from start of stall until loss of control, so it allows us to train and use only the rudder to balance the wings at low speeds). Advantage is that you get used to keep the stick centered to avoid increasing the stall playing with the ailerons and still allowing full control of bank with rudder. – maximusboscus Sep 15 '23 at 12:25

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