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?

Which aircraft type?

Gear down, Flap 20, is a call on the B777!

..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

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.

Airbus 320

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

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.

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?

Check Airman, that sounds like the Boeingization of Airbus procedures. There is no other reason for linking GD with F3.

I wouldn't doubt that at my current airline, but my previous airline has never operated Boeings.

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.

The hydraulic pumps can only supply a finite flow/pressure.

From Hursts. Airbus Technical part 14. Hydraulics

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.

Used to be a restriction at my previous airline, current has no limitations. Taking flaps 3 and full while the gear travels is SOP.

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 .