Not extending flaps while gear is extending

[Airmann]

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?

[FlyingStone]

Which aircraft type?

[FuelFlow]

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

[B-757]

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

[westhawk]

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.

[Airmann]

Which aircraft type?

Airbus 320

[BarryMG]

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

[compressor stall]

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”.

[vilas]

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.

[Check Airman]

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?

[Superpilot]

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

[Check Airman]

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

[seventhreedriver]

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.

[compressor stall]

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.

[TURIN]

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 (https://hursts.org.uk/airbus-technical/html/ar01s14.html)

[Check Airman]

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.

[Fursty Ferret]

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

[EGPFlyer]

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)

[giggitygiggity]

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 .

[Jonty]

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.

[vilas]

Manufacturer's procedures are sort of optimum covering all situations. Extending gear and flaps together is to avoid overloading the hydraulic systems involved. It's not forbidden or a limitation but a matter of good operating practice. Company procedure Gear down Flap3 may not necessarily be to overrule Airbus and a must do this way. Could easily be a case of hasty adaptation.

[InSoMnIaC]

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 .


so you “forgot to configure in time” and the captain is the one not seeing the big picture... ok

[iggy]

It is a PTU limitation and the procedure is there to cover single engine case. When in single engine the PTU is transferring HYD power from one system to another. The pressure transmitted by the PTU is 2500 PSI, not 3000 as the EDP, so the PTU is not capable of handling both gear and flaps at the same time. Following Airbus philosophy of designing procedures that are easy to remember and to follow, they decided that it would be better if they implement the rule of not operating gear and flaps at the same time in ALL situations, anticipating the fact that most pilots would forget about this in the quite infrequent case of single engine approach and landing.

The PTU limitation USED to be in the FCOM loooooooong time ago (like so many more things!), but got removed a while ago.

[safelife]

Air Berlin had a procedure to select the gear down lastest 6 NM out, and then wait for the speed to drop way down, until about 15 kt over Vapp, only then select flaps 3.
Apparently it reduces the wear on the flaps (aerodynamic loading) quite a bit.

[Dan Winterland]

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

It is. My company used the vanilla Airbus SOPs until we were bought by another which had both types and where the Boeing fleet was the legacy fleet and had primacy. Now we have had to go back to Airbus SOPs, selecting flap 3 after the gear is down is back in - although I do seem to fly with a number of pilots who haven't noticed. And there is a good reason for it. Airbus don't want the hydraulic systems overloaded as hydraulic pressure is used to both raise and lower the gear. Boeings on the other hand use gravity to lower the gear and the weight of the gear pushing the fluid out of the jack actually increases hydraulic system performance.

[Goldenrivett]

Boeings on the other hand use gravity to lower the gear and the weight of the gear pushing the fluid out of the jack actually increases hydraulic system performance.
Do you want to reconsider?
The gravity assisted gear will be pushing fluid into the return line to the Hyd reservoir. It can't assist system performance.

[Check Airman]

It is a PTU limitation and the procedure is there to cover single engine case. When in single engine the PTU is transferring HYD power from one system to another. The pressure transmitted by the PTU is 2500 PSI, not 3000 as the EDP, so the PTU is not capable of handling both gear and flaps at the same time. Following Airbus philosophy of designing procedures that are easy to remember and to follow, they decided that it would be better if they implement the rule of not operating gear and flaps at the same time in ALL situations, anticipating the fact that most pilots would forget about this in the quite infrequent case of single engine approach and landing.

The PTU limitation USED to be in the FCOM loooooooong time ago (like so many more things!), but got removed a while ago.
Hadn't considered the single engine case. Same profile in the simulator though, and no issues. I ASSUME the sim modelling is right.

If it used to be in the FCOM, it leads me to believe that it's probably an issue with older planes.

[Check Airman]

so you “forgot to configure in time” and the captain is the one not seeing the big picture... ok
I agree with giggitygiggity .

The captain lost the big picture. Mistakes happen, people fall behind, situations deviate from the ideal world of the SOP. A pilot must be able to quickly and safely adapt to a changing situation.

If they weren't stable until 1020ft, I'd say piss poor aviating and leadership on the part of the captain.

[FlightDetent]

It is not your best day when you foul up the other pilot's intention by sticking to the letters verbatim. Still a moment to learn from.

1000 ft of RA, AFE, above TDZ elev? Either way 1020 is above that. Then the hamsterwheel IMC/VMC, the latter having different legal definitions based on the airspace class etc.

BTW the Airbus' own FDM/QAR algorithms flag the CONF only at 750 ft ATDZ. And FCOM has no criteria of speed in the stable approach paragraph (both for a reason).

[Check Airman]

It is not your best day when you foul up the other pilot's intention by sticking to the letters verbatim. Still a moment to learn from.

1000 ft of RA, AFE, above TDZ elev? Either way 1020 is above that. Then the hamsterwheel IMC/VMC, the latter having different legal definitions based on the airspace class etc.

BTW the Airbus' own FDM/QAR algorithms flag the CONF only at 750 ft ATDZ. And FCOM has no criteria of speed in the stable approach paragraph (both for a reason).
Agreed 100% that it's a learning moment, but you adapt and go, and talk about it afterwards. Being pedantic for the sake of it does not achieve anything. If we're going to fault the FO for admitting that he got distracted and configured too late, the captain should also be faulted for not effectively monitoring, and catching the error earlier.

[vilas]

If it used to be in the FCOM, it leads me to believe that it's probably an issue with older planes. why the note was removed is difficult to guess but what matters is that the procedure " When flaps are at two gear down. When gear is down flap three" still remains in place. So there's some logic. If someone did something different to save a situation it can only be as an exception.

[compressor stall]

Vilas, I agree the perfect approach would have us fly the "When flaps are at two gear down. When gear is down flap three" procedure. But we know the real world is not like that, either through omission (as above) or ATC demands.

But does your A320 FCOM have the note in italics about extending the gear after Flap 2 to reduce speed as I mentioned above? Before the "When Flaps are at 2" procedure?

[vilas]

Italics off course are mine. But it's in bold letters. And we had the same procedure in A300 and A310 or in B747 for that matter.

[vilas]

compressor stall. Even QRH says the same thing.

•When FLAPS 2:
L/G DOWN........................................................ ORDER L/G.......................................................SELE CT DOWN
AUTO BRAKE.....................................CONFIRM
GRND SPLRS.......................................... ARM
EXTERIOR LIGHTS...................................................... SET
•When L/G down:
FLAPS 3....................................ORDER
FLAPS 3........................................................... ................. SELECT

[InSoMnIaC]

I agree with giggitygiggity .

The captain lost the big picture. Mistakes happen, people fall behind, situations deviate from the ideal world of the SOP. A pilot must be able to quickly and safely adapt to a changing situation.

If they weren't stable until 1020ft, I'd say piss poor aviating and leadership on the part of the captain.

Maybe he was trying to teach the FO a lesson he would never forget. Although admittedly cutting it tight, they were stable by 1000'. Whats so piss poor about that?

[Check Airman]

Maybe he was trying to teach the FO a lesson he would never forget. Although admittedly cutting it tight, they were stable by 1000'. Whats so piss poor about that?
I say poor aviating and leadership because by deliberately delaying configuration, the FO probably got unduly stressed, possibly focussing on speed, to the detriment of other instruments. Probably causing temporary tunnel vision. Reduced SA for both of them, as they're now closely watching the altimeter, counting the inches, down to 1000ft.

If he'd configured the airplane as requested, they'd have been stable earlier without the anxiety and extra crm related tension.

[madcow1]

To play Devil's Advocate, it does say "when flap two, select gear down". Do you always immediately do this, or wait for a more suitable time?

[Cough]

I'm thinking if we don't separate gear and flaps during a G/A, then it isn't an issue on the approach. The big hydraulic demand is when the gear is raised... [pure comment on technical suitability of combining both actions, not the SOP's - I hear ya Villas!]

[FlightDetent]

Cough keep in mind the aero forces on the flaps have different effect whether you are retracting or extending. Another point to consider, during GA there is no simultaneous movement of flaps and L/G. Not even of L/G doors (which are dropping down anyways).

madcow1 read that in the context of the full sequence: F2 at 2000 ft AAL. Delaying the L/G call afterwards is not really an option to meet the stabilization criteria. Moreover, F2 initially create a small speed increment and speed reduction is debatable. Only taking the gear out without delay slows you down, which helps to reduce loads on flap mechnanism more quickly.

Notwithstanding the fact that on airports where 180/160 speed control is applied, following the Airbus decelerated SOP is not a workable option.

[vilas]

Cough
I'm thinking if we don't separate gear and flaps during a G/A, then it isn't an issue on the approach. . Purely from go around perspective, we do and should separate gear and flaps. The flap is retracted from full to 3. Then FMA(which ensures TOGA&SRS) and sustained climb only then gear up. That's the lesson driven home by Dubai 777 accident. If the gear wasn't retracted it wouldn't have happened.

[FlightDetent]

I like to think that in the Airbus world the need of correct GA sequence was understood well before the EK crash at DXB. If not, the old history remember/repeat rule will apply.

The FMA and lack of GA modes is the key point, not the L/G as such. In agreement with the above, if I close my eyes the flap lever is item 2 in the sequence; the gear lever movement would be 6 or thereabouts.

[Cough]

Cough
. Purely from go around perspective, we do and should separate gear and flaps. The flap is retracted from full to 3. Then FMA(which ensures TOGA&SRS) and sustained climb only then gear up. That's the lesson driven home by Dubai 777 accident. If the gear wasn't retracted it wouldn't have happened.

For years we were flap 3, positive rate, gear up. No FMA.... Yes we overcame these yesteryear moments and instilled FMA awareness, but I can't think of a G/A from the days of the inception of the A320 series whereby a hydraulic failure was caused by the simultaneous movement of both gear and flaps. And as noted above, we have a procedure whereby both are moved, in all our aircraft, daily, IAW SOP's with little issue. Makes for a great, quiet, efficient approach. As I said above, my thoughts are technical, not SOP related.

[FlightDetent]

Even when the old ways were allowed to work :E, there was no simultaneous movement of flaps and L/G during the GA sequence. By the time pilot's hand touches the gear lever, the flaps would be well reconfigured.

Personally, I like the explanation already provided above, expanded. During approach, F2 take about 5 sec to extend against the airflow, powered by G & Y pressure delivered from one EDP in the OEI scenario. Simultanoues demand of the LG operation at that stage will cause hydraulic pressure drop below the ECAM warning level, causing nuisance warnings and god knows what other side effects in the F/CTL system. The demand is quite substantial, e.g. during normal take-off the PTU runs momentarily in support of the G HYD anyways.

To avoid the uncecessary, there used to be a note in the SOP so that the drill of extrending the flaps and gear could remain the same after an engine has given up. Exactly the way it shall be done, a good SOP set already caters for single failures.

Maybe the suggestion got removed in pursuit of operational benefits you speak of, whilst knowing no harm would be done - a simple change of heart?