Flaps question

[andreadebiase 5]

Flight school question. Under what circumstances does one need to set flaps differently from the normal/usual 30? Altitude? Wind? Can u make some simple examples? One example I can think of is high altitude landings and full flaps to compensate for lower air density but is this right? What else?

[downscc 1,327]

The FCOM does not include performance data for Flap 30 landing, but in actual operation this data is well known and used.  A heavy aircraft and a short runway will justify the consideration of Flaps 40 rather than 30, as well as reports of less than good braking action.  Think KMDW in the winter.

[Spin737 102]

High altitude airports may actually require F15 landings due to climb performance. Urumqi, China, eg. 

[skelsey 765]

As a general rule: extending flap increases both lift and drag.

As such, more flap results in:

• Reduced climb performance (more drag)
• Steeper descent angle for a given power setting/airspeed (more drag)
• Reduced stalling airspeed (more lift) and therefore reduced Vref and reduced stopping distance
• A lower nose attitude on final (more lift)

Thus, as mentioned above, more flap is generally a good idea whenever you want to reduce airspeed/stopping distance etc. I'm not sure about the 737, but on the 747 it was certainly SOP to use Flap 30 in LVOs because the lower nose attitude provides a better visual segment; likewise normally at hot and high places it would be F30 as well to reduce the TAS and therefore landing distance/brake energy but I can also see Matt's point that if you're somewhere ridiculously high you may be limited by missed approach climb gradient and thus need less flap.

For the same reason OEI landings may also be conducted with reduced flap in some types.

Some types are considered to have better handling characteristics with reduced flap (on the A320 for instance it is generally considered that the aircraft is more responsive in gusty crosswinds in Config 3 compared to Config Full) but that may not be the case for all types (or noticeable to all pilots!).

[MarkJHarris 128]

Right. 

F30 is indeed the normal landing position. It makes for a nice landing usually. Only Cadets and Training Captains can make a stinker......

F40 works on shorter runways and anything less than 2,000m it should be considered.  F40 is also normal for Autoland. 

F15 is only used for OEI landings, though newer aircraft actually have performance figures to land F30 on one engine. 

F30 autoland is not pleasant...the aircraft doesn't like it and it floats for ages. Avoid.

F15 Autoland not certified.

Pretty simple rules. 2,000m. Over it use F30, under it use F40. That's how the real world rolls!

 

[andreadebiase 5]

Thank you. This helps a lot.

I’m still puzzled about high altitude landings. Is there a rule for those for the 737 and 738.

[Spin737 102]

On 1/28/2018 at 9:42 AM, MarkJHarris said:

F15 is only used for OEI landings, though newer aircraft actually have performance figures to land F30 on one engine.

F15 is not only for OEI at all airlines. It's in the Normal Procedures section of my manual as of a couple years ago. I think American Airlines has had them for quite some time.

[MarkJHarris 128]

Interesting Matt. Was that for the -700 or -800 as well? Just wondering. Our -800s have F15 showing in performance data and it's selectable on the FMC, but I wouldn't dream of using it even on a positioning flight in an -800. Mind you, our Flight Ops Dept banned us from using F2 ever, and of course, almost all operators don't allow F1 to appear in -800 take off performance data solutions.

 

Used to fly the -700 and we did F1 departures regularly there, but never F15 landings.

[MarkJHarris 128]

I used to fly in Turkey, so landing at 6,000ft was normal. We just tended to use F40, as our landing speeds were sohing "interesting" TAS numbers. It certainly felt fast landing at VAN, LTCE, and that wasn't a particularly long runway either.

[JoeDiamond 67]

On 1/28/2018 at 11:42 AM, MarkJHarris said:

F15 is only used for OEI landings

We are authorized to do normal, two engine landings with flaps 15.  Very useful if you have strong crosswinds and plenty of runway.

[JoeDiamond 67]

1 hour ago, Spin737 said:

F15 is not only for OEI at all airlines. It's in the Normal Procedures section of my manual as of a couple years ago. I think American Airlines has had them for quite some time.

We have had it for at least five years now, if not longer.

[JoeDiamond 67]

16 minutes ago, MarkJHarris said:

Was that for the -700 or -800 as well?

737-800.

 

17 minutes ago, MarkJHarris said:

and of course, almost all operators don't allow F1 to appear in -800 take off performance data solutions.

I find this statement interesting as flaps 1 is our most common takeoff config in the -800.

[MarkJHarris 128]

Wow. Your outfit clearly doesn't employ some of the idiots mine does. Tail scrapes are far more likely with a F1 departure which is why neither of the companies I have worked for allowed them on the -800. I never really saw a problem, but I used to fly Q400 and am generally a slow to medium rotate kind of guy. Count yourself lucky you work for a laid back flight ops team!

[JoeDiamond 67]

1 hour ago, MarkJHarris said:

Wow. Your outfit clearly doesn't employ some of the idiots mine does. Tail scrapes are far more likely with a F1 departure which is why neither of the companies I have worked for allowed them on the -800. I never really saw a problem, but I used to fly Q400 and am generally a slow to medium rotate kind of guy. Count yourself lucky you work for a laid back flight ops team!

Laid back isn't the term I'd use to describe them.  Sensible would be a better description.

We do require the use of the HUD, if it's operational, for all takeoffs as an additional tail strike avoidance measure.  It really hasn't been an issue.  What few tail strikes we have had have all been on landing.

[Ralgh 43]

I think Joe and I work for the same airline. I flew the 737 for almost 14 years. We actually have had a few tail strikes on takeoff all at flaps 1. The count was five or six when I left the fleet. I flew with the guy who did the very first one actually. The interesting thing, at least the last time I heard the statistics, was that all were made by the captain. When I first started flying the 737 HUD use was not mandatory but even after it was, for whatever reason, some guys did not follow the HUD guidance. The most common reason guys had takeoff tail strikes was when they adjusted V1 for a wet runway and the rotated at the V1 call instead of the “rotate” call.