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A320 S speed question

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A320 S speed question

Old 15th Mar 2006, 13:22
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A320 S speed question

Once I was flying the 320 on a terminal are, and were requested to slow down. So I asked for F1, what led the airplane to fly at S speed, around 182kt. The APP requested the speed to be reduced to 170kt, so, as we were far from the airport, and I did not want the airplane to fly with the flaps out, I manually selected the speed at 170, thus flying below the S speed. I did so because I understood that the minimum speed I could fly in would be VLS, as, the name says, is the Lowest Selectable speed. The captn of the flight told me I was wrong, and should never have done it. That I could not fly below S speed, and, instead, had to ask for F2 and fly above F speed. Does he have a valid point ?
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Old 15th Mar 2006, 14:38
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He sort of has a point. You can fly below S speed, as u demonstrated, but from an operational point of view, I agree that u probably should have extended flaps, although I can see ur point for wanting to keep them in.

Green dot, S and F are maneuvering speeds in the selected config. So although the plane can safely be flown below the speeds in that config, you may not have adequete protection against stall for all the maneuvers that the plane is certified for. It's highly unlikely that you will have to push the plane to the edge of the envelope like that in a terminal though. He should have said that u SHOULD not fly below S speed.

VLS is the lowest speed that the autothrust will maintain. You can fly below this speed in manual flight.
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Old 15th Mar 2006, 15:10
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FCOM 3.4.10 P2 defines 'S' speed as:

Minimum speed at which the slats may be retracted at takeoff.
In approach, used as a target speed when the aircraft is in CONF 1.
Represented by "S" on the PFD airspeed scale.
Equal to about 1.23 VS of clean configuration.

I'd go along with Check Airman's spin on it - not a good idea.

Cheers,
mcdhu
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Old 15th Mar 2006, 16:13
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The operating policy in my company (BA), is to 'give consideration' to selecting flap 2 when atc request a speed between S speed and Vls on the approach.

I personally prefer this approach, ie to leave it to the pilot 'on the day'.

I think it depends on the prevailing conditions and flight profile.

Personal reasons for taking flap 2:
- above the glideslope (goes down better with F2)
- in icing (incr thrust with TAI on)
- in turbulence (better margins)
- if more than about 15kts below S-Speed

Personal reasons for sticking at flap 1:
- smooth air conditions
- more than 8nm to touchdown and below glideslope.

Just my thoughts....
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Old 15th Mar 2006, 16:46
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I agree guys/gals - normally one would extend some flap when slowing below S speed but you don't HAVE to.
There has been a couple of times I've used selected speed below S in Conf 1 following an ATC request - but only for a max of S - 10 knots and whilst flying a longish period of straight and level . Also told my F/O why and ensured he/she was aware & happy.
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Old 15th Mar 2006, 18:44
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Thanks for all the postings. Whatchdog, what hapenned with me was exactly what hapenned to you. I did not want to fly far and low having flaps down. The thought of this S speed makes me think about another thing.

Let´s say I want to make a close in turn, and select on PERF v2+10 or +20, so I can climb faster and have a minimum turn ratio. Then we would have the aircraft flying close to the ground, still with a speed under S. Would that be something wrong to do ?
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Old 15th Mar 2006, 19:14
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complicating things

Eisenhower:

Don´t try to find it in FCOM and certainly dont try it out with "that" Cpt, but how about setting Flaps 2 and back to Flap 1 so u get your flaps in 1 position (to-ff position) ?
I am not sure what might happen to S speed, probably it will remain the same, as S,F speed are computed according to flap lever position but certainly VLS will go down as it reflects the high-lift devices actual position.

Anyway, I wouldnt do it for procedure sake.
Just an option to consider, probably widely discussed and dismissed by the Airbus engineers.

Saludos
LUPA
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Old 15th Mar 2006, 19:52
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Green Dot / 'S' / 'F' partially represent the Min Drag speeds. Flying with F1 below S is "legal" in most people's books (as stated above) but not very sensible or good airmanship. Drag & Fuel Consumption will increase over the F2 situation, you are the wrong side of the "Drag Curve", you have less "buffer" from minimum speeds e.g. in the case of turbulence / wake, and apart from anything else, have an uncomfortably high nose attitude to maintain level flight....
Personally, if my P2 tries to fly anything more than a couple of knots below S with F1, I try to gently suggest F2 might be a nice idea
Just my 2ps worth
NoD
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Old 16th Mar 2006, 01:42
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Originally Posted by TopBunk
The operating policy in my company (BA), is to 'give consideration' to selecting flap 2 when atc request a speed between S speed and Vls on the approach.

I personally prefer this approach, ie to leave it to the pilot 'on the day'.

I think it depends on the prevailing conditions and flight profile.

Personal reasons for taking flap 2:
- above the glideslope (goes down better with F2)
- in icing (incr thrust with TAI on)
- in turbulence (better margins)
- if more than about 15kts below S-Speed

Personal reasons for sticking at flap 1:
- smooth air conditions
- more than 8nm to touchdown and below glideslope.

Just my thoughts....
I like this idea better tham my own. The environment in which we work is too dynamic for hard and fast rules written in stone. Assess the situation, then take appropriate action. It could be that 99% of the time, one procedure works fine, but we're paid to use judgement and call upon our experience as professionals.
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Old 16th Mar 2006, 17:23
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Thanks to everyone who posted their opinions.

LUPA, I could not do what you said, for 2 reasons:

1) It would give me a trailing edge flap, something I did not want to in order to avoid drag.

2) all acft are equipped with FOQA, what would make me and the captn go for some coffee and biscuits.
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Old 16th Mar 2006, 21:51
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Originally Posted by Eisenhower
Thanks to everyone who posted their opinions.

LUPA, I could not do what you said, for 2 reasons:

1) It would give me a trailing edge flap, something I did not want to in order to avoid drag.

2) all acft are equipped with FOQA, what would make me and the captn go for some coffee and biscuits.

What's FOQA?
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Old 16th Mar 2006, 22:35
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Looking at the original situation from a different angle, is there anything wrong with asking ATC if 180 kts, or whatever your S speed is, is OK? They are well aware that we are trying to fly as efficiently as possible to avoid making too much noise or burning too much fuel. Don't ask, don't get?
Question for ATC - would this be too much of a pain, assuming it isn't obvious you are working flat out at rush hour and the airwaves are full. Will you accept any leeway on speed without us asking, say 5 - 10 kts, if it allows us to keep a cleaner configuration for a bit longer, ?
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Old 16th Mar 2006, 23:11
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I believe the limit is +or-10kts anyway.
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Old 17th Mar 2006, 19:02
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Yep, + or - 10kt is Ok, but since there was an acft some 6nm ahead, I decided to slow down in order to allow separation.

FOQA- Flight Operations Quality Assurance. A device installed that copies info from the data recorders and compares with given values. Depending on the discrepancy, you will be called for a cup of tea.
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Old 17th Mar 2006, 19:22
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No Airline's Flight Data Monitoring program ought to pick up pilots for operating well within the aircraft envelope, as in the situation LUPA describes...just because on a 'normal' line flight we only move the flaps in one direction after we have cleaned up post-takeoff, doesn't mean that we can't! What if ATC changed their minds and asked for green dot speed (220kts?) again, after requesting 180? Would you expect FOQA to pick up on that if no limit speeds we exceeded on minimum speeds underflown?

I would expect not - b*llocking pilots who don't fly 'just so' is not what FOQA does - speak to your Flight Safety department about the system and learn about the benefits for all of us, rather than subscribe to the usual uninformed crewroom urban myths about FDM!

Now, the kind of thing FOQA may be set up to spot, is deliberately flying below manoeuvre speeds for the current configuration...that should result in a quick Q&A with the boss!

LUPA's idea might be worth trying one day, with a well-briefed crew and (ideally) a low workload situation (just so you are more able to monitor things properly!).
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Old 18th Mar 2006, 21:10
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Well, Gary, this F2 to F1 selection was discussed during the Ground School refreshment, and it was told us that FOQA had been programmed to show if that maneuver happens. I am not going to be the one going for a cup of tea, even thinking like you, that maneuvers that are on the operating limits shouldn´t be repressed. But, I am the employee, not the employer.
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Old 19th Mar 2006, 01:22
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I say cooperate and graduate, yes you can safely operate below the S speed but the majority of operators do not operate like this, your cpt is giving you correct information.
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Old 19th Mar 2006, 01:37
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From A320 Instructor Support Manual- ' You may fly below current maneuvring speed of the current configuration, provided you fly above VLS '.
Of course you can fly below S speed with Flap One out!

What do you do in case of a flapless or slatless approach, reference maneuvring speed? You fly below your maneuvring speed but > VLS.

But when you are told to fly 180kts by ATC, for example, and S speed is 185kts, most punters will happily fly high drag with flap 2.

Personally, I don't do it. The concept is poorly understood by A320 pilots. And seeing an aviator turning blue, because you are a few knots below S speed, ain't worth the hassle!

Last edited by Gnadenburg; 26th Mar 2006 at 00:39.
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Old 19th Mar 2006, 08:23
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Fair enough, Eisey - the culture in my company re: FOQA/SESMA/OPTIC/whatever you call it does not result in cups of tea very often, unless it is very obvious that negligence is a factor. Instead it is used to identify operating trends (such as pilots flying below S speed etc) and permit safety management to either a) write a fleet memo saying DO or DON'T and/or b) change SOPs accordingly and hopefully also c) allow the training department to conduct proper training/explanation of the circumstances.

Individual pilots should not to be pulled out of the ranks unless something warrants serious re-training. If that is unfortunately the culture where you work, I am sorry.

Still doesn't change my suspicion that if the FOQA picks up when F1 is reselected after F2 extension, it would almost certainly pick up flying below S speed with only F1 selected, regardless of the rights and wrongs discussed here, since whilst still within the operational envelope (as agreed here) it falls outside most companies (and so I suspect also the manufacturer's) SOPs for airmanship reasons.


So if you really want to avoid a 'cup of tea', the (somewhat flippant but still valid) response has to be:

1) stick to your company SOPs, even when you think you have a 'better' idea
2) if your fellow crewmember (Captain OR First Officer) is unhappy with the reasoning behind a proposed deviation from SOP, you have a duty to keep them 'in the loop' and comfortable with the operation; so resist trying it on this occasion! In any case see rule 1)
3) Take your suggestion to your technical pilot/chief training captain for the definitive response and (if necessary) top cover - you might be thanked for it, or you might learn something.

This issue seems broadly split on technical validity, but ought to be considered also from airmanship and CRM terms, as mentioned.

All the best,
GL
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Old 20th Mar 2006, 11:22
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Originally Posted by Gary Lager
it falls outside most companies (and so I suspect also the manufacturer's) SOPs for airmanship reasons.
From the Airbus Instructors Support Manual- "You may fly below current maneuvring speed of the configuration, provided speed is above VLS".
I would suggest this means flying below S speed is OK. But typical Airbus, have yet to, incredulously considering the price of oil, incorporated this into FCOM.

At max landing weight, your flaps jam. S speed is 182kts. Vref is 134kts. Approach increment is 25kts. Your Vapp is now 159kts. You can suffer an engine failure in this scenario and still have no restrictions flying below S speed without Flap 2!

That Airbus pilots are uncomfortable flying a few knots below S speed, is testament of how much the French are dumming down this profession.
Flying a level segment, with high drag Flap Two, burning an extra 20kg a minute, to meet an ATC speed requirement is poor airmanship IMHO.

I am confident Airbus will incorporate the practice of flying below S speed without Flap 2, when the price of oil makes 'green' approaches all the fuss.
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