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Not extending flaps while gear is extending

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Not extending flaps while gear is extending

Old 7th Feb 2019, 08:32
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Not extending flaps while gear is extending

Had a Sim recently where the instructor was adamant about not extending flaps until gear extension was completed. But never got a satisfactory answer as to why.

Anyone have an answer?
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Old 7th Feb 2019, 08:39
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Which aircraft type?
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Old 7th Feb 2019, 08:54
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Gear down, Flap 20, is a call on the B777!
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Old 7th Feb 2019, 08:58
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Originally Posted by Airmann View Post
Had a Sim recently where the instructor was adamant about not extending flaps until gear extension was completed. But never got a satisfactory answer as to why.

Anyone have an answer?
..If such limitation exists, it would be found in the aircraft manual..If not, your instructor is teaching you his own procedures..

Fly safe,
B-757
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Old 7th Feb 2019, 09:35
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How much flaps?

If it's FULL flaps, I agree with the instructor. Bad form with the gear not down & locked. Plus I'd like to preserve what's left of my hearing!

The sim profiles are a useful template for speeds and configurations to achieve during each the various segments of an approach. Most jets have one or more increments of flaps deployed before gear extension. Gear extension is often delayed until just outside the FAF or GS intercept. Now, with the gear down and green, landing flaps can be selected for the final approach without all that noise!

Of course each type has it's own manufacturer recommended profile and operators differ as to some of the specific SOPs and techniques, but the idea is to be on profile and in a good position to maintain a stabilized approach. In practice, the timing of flap and gear extension can be adjusted in concert with the noise levers to account for variables such as visuals, slam dunks, short intercept vectors or speed assignments! But keeping those profiles in mind as a template for where "normal" should be gives you something to compare against your actual progress.

If you know each of the sim profiles cold, sim training goes allot more smoothly. When you get on the line, that's when it all comes together and pays dividends. Enjoy.
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Old 7th Feb 2019, 09:37
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Originally Posted by FlyingStone View Post
Which aircraft type?
Airbus 320
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Old 7th Feb 2019, 10:24
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If it's A320 then it's quite simple - both gear and flaps are hydraulically powered. While the systems (especially pumps) are perfectly capable of operating both at the same time, it may be wise not to demand too much from them at once - if not to avoid sudden failure (which is most likely to occur during such high-load scenario) then simply to reduce wear and tear
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Old 7th Feb 2019, 11:23
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Are there any Airbus references for that theory? Or any statistical data ? What happens in a go around?

Or or are people just [cue best Monty python voice] “making it up as he goes along”.
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Old 7th Feb 2019, 14:36
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Had a Sim recently where the instructor was adamant about not extending flaps until gear extension was completed. But never got a satisfactory answer as to why.
The answer is in FCOM normal procedures. During approach it says "Flaps 2, when flaps are at 2 gear down". It further says "when gear down Flaps 3". You say Flap2 when the number becomes blue to confirm SFCC has got the order but you lower the gear only when flaps are extended to two. Similarly you announce gear down when you see three reds to confirm LGCIU is lowering it but you only select flap3 when the gear is actually down that's when three green. The instructor was right. Even the Airbus PDP displays the same.
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Old 7th Feb 2019, 16:05
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Thanks vilas as usual for your insight (and reference).

Both A320 operators that I've been at have "gear down flaps 3" as a std config change callout. Never heard of anyone having trouble. Perhaps some older aircraft had an issue?
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Old 7th Feb 2019, 17:11
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Check Airman, that sounds like the Boeingization of Airbus procedures. There is no other reason for linking GD with F3.
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Old 7th Feb 2019, 19:28
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I wouldn't doubt that at my current airline, but my previous airline has never operated Boeings.
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Old 7th Feb 2019, 19:56
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Just a guess as to why: both the gear and the flaps/slats are downstream of the HYD priority valves, and if these two systems simultaneously demand high load in less than ideal circumstances, the prio valves might end up locking them out of the system for a bit, resulting in mismatch between the desired and the actual config for a few seconds. Not being a proper engineer, this would be my guess.
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Old 7th Feb 2019, 20:09
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Villas, agree with the wording for normal SOPs, and it’s the aim for the perfect profile.

However on my A319, the F2 selection is followed immediately by the following note...
If the aircraft speed is significantly higher than "F" speed on the flight path, or the aircraft does not decelerate on the flight path, extend the landing gear in order to slow down the aircraft. The use of speed brakes is not recommended.
no instructions to wait.

The normal “when flaps are at 2” is in the subsequent section.

But is there a restriction / limitation / prohibition on putting the gear out when the flaps are travelling (eg “XXX, reduce to min approach speed immediately “)? (or vice versa) I can’t see hydraulics being a limitation, again, in a go around the gear is often coming up as the flaps are travelling up one stage.

Last edited by compressor stall; 7th Feb 2019 at 21:17. Reason: typos
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Old 7th Feb 2019, 20:26
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The hydraulic pumps can only supply a finite flow/pressure.

Each system also has a priority valve to cut off heavy users (flaps, slats, gear, emergency generator) if system pressure gets too low to operate the flight controls.
From Hursts. Airbus Technical part 14. Hydraulics
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Old 7th Feb 2019, 21:04
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On the topic of overloading the hydraulic system, occasionally (usually on older planes) I'll hear the PTU during gear retraction while in the cabin. Never noticed it during extension.
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Old 7th Feb 2019, 21:22
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Used to be a restriction at my previous airline, current has no limitations. Taking flaps 3 and full while the gear travels is SOP.
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Old 7th Feb 2019, 23:39
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I’ve always taken it that that the FCOM written in such a way to say that you ‘should’ wait for the gear to be down before selecting F3 but not that you ‘must’ (i.e. there’s no limitation)
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Old 8th Feb 2019, 01:18
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Originally Posted by EGPFlyer View Post
I’ve always taken it that that the FCOM written in such a way to say that you ‘should’ wait for the gear to be down before selecting F3 but not that you ‘must’ (i.e. there’s no limitation)
Precisely, if it was a limitation, it would be in the FCOM-LIM. Years ago I remember a good captain denying me flaps 3 whilst the gear was travelling (after admittedly I forgot to configure in time). We finally selected flaps full out at about 1020ft (so 20ft away from our approach gate) to satisfy his limitation. People get so caught up in this crap that they totally miss the big picture. He would have probably rather have executed a go-around than 'stressing' the hydraulics .
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Old 8th Feb 2019, 01:45
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Originally Posted by giggitygiggity View Post
Precisely, if it was a limitation, it would be in the FCOM-LIM. Years ago I remember a good captain denying me flaps 3 whilst the gear was travelling (after admittedly I forgot to configure in time). We finally selected flaps full out at about 1020ft (so 20ft away from our approach gate) to satisfy his limitation. People get so caught up in this crap that they totally miss the big picture. He would have probably rather have executed a go-around than 'stressing' the hydraulics .
Or you should learn to configure in time.
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