First we take flaps 1 then 2 after that we lower the gear followed by flaps 3 and full. My thinking is that this will avoid any GPWS warning is that it or there is something else also to it.?

  • $\begingroup$ The procedure is somewhat similar in small GA aircraft with retractable gear. I was always taught that the sequence was "flaps-flaps-gear-flaps" and then another gear check on short final. $\endgroup$ – Ron Beyer Sep 7 '17 at 14:43

You would want to start with flaps/slats. The landing gear slows the aircraft down like an airbrake, and you'll need a higher lift coefficient to retain enough lift. Slats are a safety feature that allow for a higher angle of attack for the main wing, flaps provide a higher $C_L$ by themselves. So you start with a higher $C_L$ and the safety of the slats, then deploy the gear which slows you down, then delay more flap/slat at the lower velocity.

Deploying full flap/slat first and then deploying gear is also not a good idea: speed will be slow already at max flaps, gear deployment brings a significant further deceleration which may have an impact on safety, definitely on continuity throughout the landing process. You are in a queue with lots of others at a busy airport, and want to keep the array of craft flowing without sudden decelerations.

  • $\begingroup$ I know each aircraft will have Vmax limits for each config. Is the flaps/slats limit usually higher than the gear limit? And is the gear limit usually higher than flaps full? $\endgroup$ – TomMcW Sep 7 '17 at 17:45
  • $\begingroup$ I reckon the procedure is just for Best Practise. It could probably be done in a different order without breaking the aircraft, but the procedure of the OP makes the most sense. $\endgroup$ – Koyovis Sep 8 '17 at 6:04
  • $\begingroup$ Found an A320 manual online. VLE/VLO are 280/250kt and VFE is 230kt for the 1st position (slats only). So you're correct, it's not due to design limits $\endgroup$ – TomMcW Sep 8 '17 at 17:48

this is speculation, but if you ask why we lower gear between F2 and F3, I think Koyovis is getting quite close to the potential answer:

Each configuration has a reference speed: Green Dot, S speed, F speed. The biggest difference is between S and F ( ie after deploying flaps 2) , that is: this is where aicraft will decelerate the most from around the 180+ kts S-speed to the ~140 something F-speed.

This can take quite a while to decelerate, so it might be a good ideea to use this time to lower the gear (since hydraulics are now free) and even use that extra drag from gear to decelerate.

Mind you, you can still lower the gear at the same time as lowering the flaps, it's just extra strain on the hydraulics so most people will try to avoid making that habit.

Also, remember it is not prohibited to lower the gear much earlier ( eg. if you require extra drag on the approach), even in clean config.There used to be a limitation of FL250 for deploying gear, but that has recently been removed.

You could also delay gear down until after flaps full if there is an operational necesity. The only real limitations is to be below Vloe (250kts/M0.60) and you should try to get gear down preferably before GPWS kicks in (750ft)

  • $\begingroup$ There used to be a limitation of FL250 for deploying gear Are you talking about a regulatory limit? In the US? $\endgroup$ – TomMcW Sep 7 '17 at 17:42
  • $\begingroup$ @TomMcW , no it was an Airbus 320 limitation in FCOM $\endgroup$ – Radu094 Sep 8 '17 at 17:13

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