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Adding a 'Couple-a-Knots'
Honestly, I'm sick of guys asking me if I want to add a couple of knots to my approach speed. Honestly what difference does a couple (i.e. two) knots make. If you're going to add anything add at least a minumum of 5.
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You tell 'em champ! :ok:
PS: what about "a few knots"? |
Haha! Yeah I remember some guys won't even ask me and just forced a new higher VAPP and telling me how much it's going to save the day... :} I also like to add a few knots ( 2 to 3 knots) on the old birds. Especially A319 in conf 3 to lower the nose when the pitch is ridiculously high or on the old A321 when the VAPP is too close to VLS. 1kt is roughly 1 tonne, and few knots seem to work fine for me. I never question the VAPP of my colleagues tho. Should be a personal choice; Not a mandatory thing.
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Well it all depends. In most A320's, the fms and flight control computers calculate the speeds independently. When there's a difference, we're invariably heavier than we think we are, and thus the FMS wants to fly at a slower speed than is appropriate. In that case, I'll add another 2 or 3 kts to maintain the proper ref+5. |
Yeah. Just as a reminder: On the old aircraft VLS displayed on PFD is based on the AOA sensor ( reality) versus VAPP calculated by the FMS based on the figures inserted from the load sheet ( not very accurate eg: Assuming 75kg for adult uh huh :E) If VAPP is less than 5kt from the VLS, it means the aircraft is heavier than we (FMS) think we are, like Check Airman mentioned. I also like to keep 5kt rom VLS. Give you a nice margin in case you flare too high.:}
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In my day, flying 1st generation heavy jets I always flew VREF + 10kts, easing back to VREF "over the fence". The reason I always gave for this was, it is easier to loose the access speed should the need arise. Try recovering from a sudden 10 knot speed loss when flying VREF.. Also your landing weight maybe higher than you thought. Prevalent during cargo ops..
These days one would probably be reported for an "unstabilized approach" or some other misdemeanor, for the above. |
@ pinteam & Check Airmen: Do not worry, everyone has been through that stage.
Airmann: I am not the most experienced, but never has my landing been made any better or worse by fiddling with the numbers. The sentiment of your post is fully shared, sir. |
The reply to the query “… if I want to add a couple of knots to my approach speed” could be:- ‘What’s the correction to the landing distance?’ A numerical answer is an opportunity to debrief the risks in approach and landing, distance margins, accuracy of declared runway state, etc. Not providing an answer leads to a wider discussion on balancing risks, particularly the combination of speed and touchdown position, and thereafter stopping distance, wet runway, and overruns. https://www.skybrary.aero/bookshelf/books/900.pdf table 6, page 11 |
The reply to the query “… if I want to add a couple of knots to my approach speed” could be:-
‘What’s the correction to the landing distance?’ Is the landing roll not effected more by ground speed at touchdown than approach speed in the air? Notice I said roll because of course distance includes a short air distance where the excess speed is being bled off. |
It's not a written procedure to add a few knots. I suppose it'd fall somewhere between airmanship and technique. I don't think an FAA inspector in the jumpseat would fault a crew for increasing Vapp when it's sitting right above Vls. I've heard of one person (thankfully not at my airline) who uses ref+10 all the way to 50ft even in calm wind, all in the name of smoother touchdowns. That's something else entirely. |
All good poimts.
We were on approach once behind a heavy, dead calm (too calm?). In the blink of an eye we lost 10kts. It only needs to happen once, when you're not prepared...... |
In my day, we used to say: "Add five knots for the Wife, and five for your Pension".
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Normally added on the A319s because the VS calculated in the FMGC isn't the same as the VLS on the PDF, thus an increase in Vapp speed to make sure at least +5 VLS speed is flown. A320s are better at having a similar VLS on the PDF and calculated on the FMGC
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The question is, WARNING - this will go in direction of safetypee's post - what makes us feel so confident that it is the VLS that shows correct value and FMS+LDS speed is the wrong one?
Bonus: What is the certified approach speed? Is it Vref = VLS? |
As per QRH, we are allowed to increase up to 15kt above VLS. It’s really up to you. Everytime I increase the VAPP, I insert it in the Flightsmart landing data to have an accurate landing distance. Unless I operate on short runways ( which we don’t; the shortest one is about 2500 meters), I rather approach slightly too fast than too slow and ending on the backside of the power curve. My worst landings were most of the time due to lack of energy. |
Adding speed due to incorrect VAPP calculations in the FMS I understand. Adding a few knots in order to lower pitch attitude in config 3 also makes sense to me.
But primarily I see the addition of 2 knots (and it's almost exactly that amount) due to gusty conditions even in VREF is correctly calculated. Firstly an Airbus has GS mini function which takes care of ensuring that a margin is added when there is a headwind on approach higher than that expected on touch down, so that you don't get caught out with the wind drop. Secondly VLS is an Airbus systems speed. It is not a structural or aerodynamic speed. Going a bit under VLS is not the same as going below green dot at high altitudes. And even if you do, at lower levels all commercial Aircraft with all engines running have plenty of power to get themselves out of the back end of the curve, and so dropping a couple of knots into VLS has no real meaning except frightening some pilots. All your really doing by adding two knots is to increase your margin vs stall speed. But will 2 knots save your life? Are pilots getting a bit too paranoid here? |
RAT, #10, Is the landing roll not effected more by ground speed at touchdown than approach speed in the air? I do not believe that it is because of the multiple effects of the increased air distance. The key point is the increase in air distance due to the change in approach speed compared with that assumed in original landing performance (at the same wind speed). The change in airspeed / ground speeds are relative, although V squared is important during rollout. The increased airspeed effects both the flare time and distance, plus any float due to the higher speed than required for the weight. When compared with the expected performance, based on an idealised landing profile based on Vref, then the aircraft would be both faster and further down the runway at touchdown. Conversely, to retain the same safety margin assumed in the calculated performance, then the aircraft has to shorten the flare time to achieve the same touchdown point, and lose more speed - a fatuous argument where the limit would require a no flare landing with instant speed reduction. Therefore any unaccounted speed increase reduces the safety margin assumed in the baseline landing distance. Note Appx 1, para h (2) on page 6, - re adding speed: AC 91-79A Change 1, ‘Mitigating the Risks of a Runway Overrun Upon Landing’ https://skybrary.aero/bookshelf/books/3606.pdf And note para j (3), page 8, - re minimum acceptable safety margin. |
Originally Posted by pineteam
(Post 10157523)
Unless I operate on short runways ( which we don’t; the shortest one is about 2500 meters), I rather approach slightly too fast than too slow and ending on the leftside of the drag curve.
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Check Airman, #11, I don't think an FAA inspector in the jumpseat would fault a crew… …providing they consider / adjust the landing performance; or … unless the aircraft stops in the overrun. (JT, add FAA inspectors to the lawyers who can be found in the long grass at the end of the runway ;) ) |
I don't think it's paranoid behaviour at all. When I see Vapp sitting just above Vls, the airplane is telling me that the assumed weights are wrong. Will we die if the adjustment isn't made? Probably not, but unless we're going to a short runway, I don't see the harm in flying the speed the airplane thinks I should be flying, as opposed to the speed the load agent thinks is appropriate. Standing by to be corrected if my understanding of the Vls/Vapp determination is incorrect. |
Originally Posted by Airmann
(Post 10157551)
All your really doing by adding two knots is to increase your margin vs stall speed. But will 2 knots save your life? Are pilots getting a bit too paranoid here?
Originally Posted by FlightDetent
(Post 10157572)
Pin, say again what is the speed for bottom point of the drag curve for a 60 t landing weight?
I have no idea! Green dot speed I beleive? What I know is that getting below VLS is looking for trouble.:} Edit times 10: I see, what I said is not really correct in my previous post but you understand what I mean: Slower, more drag then more thrust required to maintain VAPP... Or should I go back to the book? xD I was referring to this graph page 5. From what I understand, a speed below VAPP and you are on the backside of the power curve. https://www.slideshare.net/syedviqua...3-presentation |
Exactly the point. Vls=Vref=Vapp.
+ 1/3 of the reported head wind for the reduction in of its speed in the boundnary layer below the anemometer height or + 5 kts if A/THR used (to allow for its speed drops not expected to exceed -5 kts) So, if the displayed Vfms is Vls+3, without really knowing which is correct, why add 2 kts? Worst case it is still Vref+3. @CheckAMN: all good until you start to develop a "long landing standard" technique. Then one day going into a short-ish place people opt for a "short landing technique" (which should have not need to exist in the first place!!!). And it scary to watch them fail their first attempt at executing what they did not practice before, and actually, they have no idea or guidance what it should be like. But as long as the shortest LDA is 2500 m, the discussion is admittedly academic. Unless one's ready to see the broader views presented by safetypee above. Similar to going for 3 red's on the PAPIs, boss. |
Ok thank you FlightDetent. But I don't know if you flew on the very old A321-100 and some -200 models with the wingtip fences: The flare is quite challenging and scary when the speed is only 1 or 2kt above VLS. Maybe it was a problem with the flight control computers but they were famous for hard landings. xD The one with Sharklets on the other hand, increasing the VAPP is looking for a very long flare. They are good gliders. :}
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Originally Posted by FlightDetent
(Post 10157588)
Exactly the point. Vls=Vref=Vapp.
+ 1/3 of the reported head wind for the reduction in of its speed in the boundnary layer below the anemometer height or + 5 kts if A/THR used (to allow for its speed drops not expected to exceed -5 kts) So, if the displayed Vfms is Vls+3, without really knowing which is correct, why add 2 kts? Worst case it is still Vref+3. @CheckAMN: all good until you start to develop a "long landing standard" technique. Then one day going into a short-ish place people opt for a "short landing technique" (which should have not need to exist in the first place!!!). And it scary to watch them fail their first attempt at executing what they did not practice before, and actually, they have no idea or guidance what it should be like. But as long as the shortest LDA is 2500 m, the discussion is admittedly academic. Unless one's ready to see the broader views presented by safetypee above. Similar to going for 3 red's on the PAPIs, boss. |
Originally Posted by Check Airman
(Post 10157576)
I don't think it's paranoid behaviour at all. When I see Vapp sitting just above Vls, the airplane is telling me that the assumed weights are wrong. Will we die if the adjustment isn't made? Probably not, but unless we're going to a short runway, I don't see the harm in flying the speed the airplane thinks I should be flying, as opposed to the speed the load agent thinks is appropriate. Standing by to be corrected if my understanding of the Vls/Vapp determination is incorrect. read my post again. Correcting VAPP for a incorrectly calculated FMS VLS is something I don't disagree with. The issue is with guys adding 2kts ONLY above VLS+5 for gust wind |
Its in interesting question that divides opinion at my firm. As far as I am concerned, the landing speed is Vls. We need 5 kts for the Athr in managed speed because its very tolerant to small variations from the target. So generally, I'm not concerned about at target speed close to Vls - the Athr is going to respond if we get below that hockey stick. I do however understand those who have got into the practice of landing at FAC Vls +5 - to each his or her own. But please please please, check the speeds as part of your descent prep, brief what you want to see on the PFD, especially if you expect your colleague to land at a particular speed, and check them during the initial approach. Check S speed from PFD and MCDU - that will tell you any discrepancy away from the ground. 800ft and IMC is not the time to be heads down fiddling with speeds in the mcdu, especially if one is PF at the time, and particularly if your colleague has no idea what your doing, and has no desire for your amendments...
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Scary thing is that as airlines transition entirely over to EFBs for landing performance there will come an entire generation of pilots that will not be made to do approach speed calculations using paper and might well have no idea of why the VAPP is what is, or at least specifically how it is calculated and the nuances of it. I believe that there are absolutely no paper performance charts at all for the 350.
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Originally Posted by Airmann
(Post 10157638)
read my post again. Correcting VAPP for a incorrectly calculated FMS VLS is something I don't disagree with. The issue is with guys adding 2kts ONLY above VLS+5 for gust wind |
How much does the pitch attitude drop if you go 2-3 kts faster on approach? On a typical landing how much additional pitch is there before you have a tail strike? |
I'm all in favor of people flying precisely. We're all professionals and sloppiness is simply not acceptable from anyone given the responsibility of people's lives in their hands. For that reason anyone correcting VAPP for incorrect FMS calculations is fine with me.
However, we all know that Airbus (I won't speak of Boeing as I haven't flown them) would like thrust variation to be as few and as gentle as possible due fuel savings. And I'm sure anyone that has flown the 320 family has experienced being in cruise and suddenly having the thrust jump forward because the aircraft has reached cruise attitude minus 50 ft after a shallow decent in an effort to increase speed without adjusting thrust but which inevitably did not yeild a sufficient increase in speed (called soft cruise or something that like). However, is anyone aware of just how the auto thrust behaves during an approach. Does it try to be gentle down to VAPP -5 Kts and then kick in hard, or does it wait for VLS? Or is there no difference at all? As for those flying manual thrust (rare these days I know) if you add 2 or 3 kts to give yourself more margin to VLS what is that saying about your trust in yourself. In a calm wind your VAPP should be VLS. And most checks call for a tolerance of only VAPP -5kts. What does it say of our own confidence in our flying skills when people do not have full confidence on the line to meet the standards they are expected to meet. |
Honestly who cares? If they ask you and you don’t want it just be polite and say “no thanks” On the a320, In my experience on newly built aircraft, the autothrust responds very slowly at low / intermediate thrust settings and in managed speed will quite often hover at the speed target - 2 or 3 knots. I have seen this on approach fully configured with the speed staying a bit below commanded Vapp. In this case I will ask for the Vapp to be increased by a few knots so the aircraft is flying at the speed it’s supposed to be at. I’d rather be a bit fast than a bit slow. Just big picture stuff. And no, unless the LDA is limiting I wouldn’t recalculate anything. (,”) |
Originally Posted by misd-agin
(Post 10157778)
How much does the pitch attitude drop if you go 2-3 kts faster on approach? On a typical landing how much additional pitch is there before you have a tail strike? https://ibb.co/fb4jY8 Flew this morning on A319. As you can see, VAPP config 3 initially is only 2.5kt above VLS and the pitch is around 6 degrees. It was fluctuating between 5 to 7 degrees. Later on, the Fo requested 2kt extra and the pitch was about 5 degrees. Only 2 kts extra made a small but noticeable difference on the pitch. on A319, a tail strike will occur at a pitch of 13.5 degrees with landing gear compressed. |
I seem to recall that there used to be a note in the FCOMs that the AOA calculated speeds were only accurate to +/- 3 kts so a lot of this seems to be academic especially since one can fly safely at VLS with manual thrust!
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Originally Posted by Meikleour
(Post 10158259)
I seem to recall that there used to be a note in the FCOMs that the AOA calculated speeds were only accurate to +/- 3 kts so a lot of this seems to be academic especially since one can fly safely at VLS with manual thrust!
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At the end of the day, in my opinion, it comes down to technique and personal preference. This is an academic discussion really. With the buffers built into line operations, 2-3 kts won't cause a stall or runway overrun. |
ML, #32. I appreciate a practical approach, assuming that your ‘who cares’ refers to the question and not the speed. Taking a more philosophical, pedantic view for discussion, how would pilots know if the new landing performance will not be limiting, particularly if based on the current calculation ? This issue reflects a much wider problem in modern operations, airmanship, professionalism. Lack of precision #31, experience #28, systems and aircraft knowledge, and the effect of external influences - FDR, SOPs, error, blame. We might learn from Bertrand Russell “I would never die for my beliefs because I might be wrong”. Are pilot’s nowadays betting their careers on belief more than knowledge; 2 or 3kts of belief or personal preference. We train in simulators - we cannot die, small deviations are accepted (the error is necessary in order to learn), but we rarely learn; instead we take to the air with the attitude that small deviations are OK, which of course can escalate to accepting situations without actually knowing the margin in operation between safety and ‘death’, loss of licence. Are we lacking risk management skills because we don’t know, don’t’ care to find out, don’t plan ahead, or fail to ask a question; the response at #9 might be the better question for the owner of originating query #1 to ask of her/himself. |
The "who cares" was directed at being asked the question if they would like a few knots added and getting agitated for being asked the question. I'm all for flying as precisely as is practical. Splitting hairs over 2 or 3 knots fast is going overboard (in the context of adding to Vapp if your LDA isn't limiting) again in my opinion only. I hardly think It speaks to any kind of unprofessionalism, or lack of knowledge either. I would consider it being assertive and doing your job properly by watching what's happening on your instruments and making adjustments as deemed appropriate. There is a very good reason that buffers are applied to speeds in the AIP and to stabilized critera for landing. |
Originally Posted by Check Airman
(Post 10158283)
At the end of the day, in my opinion, it comes down to technique and personal preference. This is an academic discussion really. With the buffers built into line operations, 2-3 kts won't cause a stall or runway overrun. |
May I add a few words. ”measure it with a micrometer, cut it with an axe”. Safe flying. (context: Australian, 737) |
Originally Posted by Meikleour
(Post 10158259)
I seem to recall that there used to be a note in the FCOMs that the AOA calculated speeds were only accurate to +/- 3 kts so a lot of this seems to be academic especially since one can fly safely at VLS with manual thrust!
Simply put it is far far far more forgiving with a ‘couple of knots’ extra. Sure you can fly at VLS, but you give away a lot of handling margin for what, 60 meters less landing distance? |
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