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?
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Gear down, Flap 20, is a call on the B777!
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Originally Posted by Airmann
(Post 10382644)
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? 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. |
Originally Posted by FlyingStone
(Post 10382650)
Which aircraft type?
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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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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”. |
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. |
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.
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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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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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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. 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. |
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. |
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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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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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) |
Originally Posted by EGPFlyer
(Post 10383615)
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) |
Originally Posted by giggitygiggity
(Post 10383666)
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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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.
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Originally Posted by giggitygiggity
(Post 10383666)
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 |
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. |
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. |
Check Airman, that sounds like the Boeingization of Airbus procedures. There is no other reason for linking GD with F3. |
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. The gravity assisted gear will be pushing fluid into the return line to the Hyd reservoir. It can't assist system performance. |
Originally Posted by iggy
(Post 10383852)
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. If it used to be in the FCOM, it leads me to believe that it's probably an issue with older planes. |
Originally Posted by InSoMnIaC
(Post 10383804)
so you “forgot to configure in time” and the captain is the one not seeing the big picture... ok 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. |
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). |
Originally Posted by FlightDetent
(Post 10384296)
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). |
If it used to be in the FCOM, it leads me to believe that it's probably an issue with older planes. |
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? |
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.
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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 |
Originally Posted by Check Airman
(Post 10384229)
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. |
Originally Posted by InSoMnIaC
(Post 10384773)
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?
If he'd configured the airplane as requested, they'd have been stable earlier without the anxiety and extra crm related tension. |
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? |
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!]
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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. |
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. |
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