Performance Vref Question

[Edgington]

This morning I sat the performance exam, scored 97% for now.

One question we all had wrong, was the following:

Approaching in turbulent wind conditions during manual flight requires:

A) An increase in VREF
B) No Change
C) A steeper approach path
D) An increase in approach speed

The answer we all gave was A, but correct answer should be D.
Can some help me understand why A isn't also correct?

[Blueskyrich]

At a guess, I would imagine that VREF is a nominated (i.e. fixed) speed based on various known factors such as weight, icing conditions etc.

Thus, as it a calculated figure, it isn't something that can be just changed. As a slightly higher IAS is needed to keep a few more knots in the bag, an increased approach speed should be used.

I think (and hope) this is right!

[kwachon]

Vref - the reference indicated (CAS (http://en.mimi.hu/aviation/cas.html)) approach speed (http://en.mimi.hu/aviation/approach_speed.html), usually about 1.3 to 1.5 times Vso plus 50% of the wind (http://en.mimi.hu/aviation/wind.html) gust (http://en.mimi.hu/aviation/gust.html) speed (http://en.mimi.hu/aviation/speed.html) in excess of the mean wind (http://en.mimi.hu/aviation/wind.html) speed (http://en.mimi.hu/aviation/speed.html).

[G-SPOTs Lost]

Vref is 1.3 x VSo and normally is the speed to be achieved by the very latest of 50ft, the idea being that you bleed off the 0.3 by touchdown

Its fixed for a given configuration and for that configuration only changes with landing weight - not wx

The other gotcha is talk of increasing Vapp - which some people consider to be an approach speed - but its not its actually there to ensure you make a gradient in the go around scenario

So to get back to the Q. its D as all you would do is be stable down the approach at Vref + 10 + (X) as opposed to Vref +10.....where X can be any number of things - 1/2 the max gust capped at 20, 10knts, 20knts all depends on your ops manual and how brave you are feeling and how strong the wind is blowing!!!

[Edgington]

Thanks for the answers, thinking it trough I understand why that is the better answer.

It is a question which has been removed from the Bristol db, and replaced with the same question but without D as a possible answer. In which case increasing Vref is the right answer, any one know why it was removed?
I know some want to appeal the question.

[Blueskyrich]

Actually, thinking about it futher, G-SPOT is on the money.

I fly the Dash 8, and we have two 'VREF' speeds for a given flap configuration and landing weight - one for icing, one for non-icing conditions. In reality though, the non-icing speed is the actual paper VREF whilst the icing speed is, in reality, an increased VAPP. Where we operate to aerodromes where a increased climb gradient is required in the event of a go-around, we used the icing speed for approach as it'll give us the ability to make the required climb gradient should we need it.

[lolopilot]

Usually, VREF is the IAS you want to achieve when crossing the runway threshold or very slightly before. As such, VREF does not change with the wind.It is a given value for a given temperature/weight/aircraft configuration. Conversely, VAPP = VREF + whatever wind/gust factor correction is the speed at which you fly the approach and it is that speed that changes as a function of the wind. As such, answer D is the proper answer.

[Lightning Mate]

Edgington,

..."scored 97% for now"...
How do you know that?

..."One question we all had wrong"...
How do you know that?

..."but correct answer should be D"...
How do you know that?
..and if you knew that, why did you opt for A?:ugh:

[Rusty Shagman]

Edgington

I wrote the same exam in Maastricht. Scored 100% and got that question right. The reason that Vref is the wrong answer is simply that the Vref does not change due to wind. All that does happen is that the pilot applies a wind correction factor (usually something like half the steady HWC plus all the gust, to a max value of 20kts, depending on aircraft type) to the Vref for the approach. :ok:

Lightning Mate

If you knew anything about how the JAA ATPLs are administered (by the CBR) in Holland, the arrogance of your last posting might be reigned in! :}

[Edgington]

Edgington,

..."scored 97% for now"...
How do you know that?

..."One question we all had wrong"...
How do you know that?

..."but correct answer should be D"...
How do you know that?
..and if you knew that, why did you opt for A?:ugh:
I'll try to explain, here in Holland, you get an extra sheet of paper to write your answers on for you to take with when you leave the exam room. Then when the exam time has passed they hand out the answers, which you can then check and calculate your score.

Why I know we all got it wrong because they others said they also filled in A?

Think I've answered the last one by now.

Anyway in England it has been succesfully appealed and the question removed from the db.

@Rusty you lucky devil, but in turbulent weather wouldn't you select less flaps?

[PAPI-74]

It is a question which has been removed from the Bristol db, and replaced with the same question but without D as a possible answer. In which case increasing Vref is the right answer, any one know why it was removed?
I know some want to appeal the question.

This is a perfectly normal and everyday situation that they have asked you.
Your approach speed is eg Vref+10 and +15 in gusty conditions - or did Bristol just tell you to memorize instead of think. Another reason why you don't learn the feed back, or when you start your IR, why you don't learn 3 routes off by numbers. You will not learn anything any your IR will be worthless, leaving you unable to pass a sim check - and you may only get one crack at it. I bet you finished in 15 mins too. Well done!!!!:ugh:

[Alex Whittingham]

Indeed no. We appealed this question some time ago on the grounds that there were two possible correct answers. I know that the approach speed is increased in gusty conditions by a margin not unlike that described above. Whilst I haven't flown them myself, my Performance instructor was an FE on BA and Virgin 747 classics and he says that on these aircraft not only was the approach speed changed but also the Vref bug on the ASI was moved to a higher speed in gusty conditions, something kwachon alludes to above. The CAA agreed there were two possible answers depending on type and said they had removed the question. Clearly it has slipped back in, possibly as a result of a new performance 'expert'.

Just to cut the sniping, we would never recommend just learning questions and answers. The sad reality is that, even if you understand the subject, the quality of the JAA questions is so poor that you often get the wrong answer. That's why the question banks are needed. Oh, and Lightning mate, don't bother. This is not a sales pitch.

[Rusty Shagman]

Edgington

Thanks buddy. Luck always plays a part in these beaurocratically determined event outcomes and I'm sure to be first to admit that.

I think what you might have overlooked in the question was the fact that it referred not only to turbulence, but also to wind: "... turbulent wind conditions ...". To me, that translated (in beaurocrat speak) to gusty conditions, in which case one simply bugs the predetermined wind correction factor. Let's not forget that airlines, authorities, and manufacturers actually determine how we deal with these scenarios, and when we take it upon our shoulders to do something else and the outcome is not the desired event, we wind up chatting to judges.

Having said that, perhaps if one were looking at "turbulent wind conditions" with a heavy landing weight which might in itself compromise flap load relief on approach, or come close to max x-wind component, I certainly would, as you rightly suggest, consider a lower landing flap setting.

By the sounds of things your exams went well. Here's to your career! :ok:

[JB007]

Generally, Vref+ a wind additive of a minimum 5 knots. The rule is 1/2 the wind, all of the gust up to a maximum of 20 knots, could differ with type!

i.e. for 270/10G20 = you'd add 15 knots to a fixed Vref figure.

[Edgington]

Thanks Rusty. Hope your exams are going equally well!

I'm kicking myself for getting this one wrong and I can't let go..... yet. And why because I followed the answer in the db, no offence to those who put the db together they have done a superjob. So PAPI-74 is right I blindly followed the db.

My first line of thought was less flaps, higher speed on the approach. Less flaps increases your Vref doesn't it? But that wasn't a possibility in the db so remembered the answer given and since then have been :ugh:
And thinking about it if fly a higher speed on the approach, won't your speed over the threshold be higher? Or do we slam on the breaks to cross the threshold at Vref?

[G-SPOTs Lost]

My first line of thought was less flaps, higher speed on the approach. Less flaps increases your Vref doesn't it? But that wasn't a possibility in the db so remembered the answer given and since then have been
And thinking about it if fly a higher speed on the approach, won't your speed over the threshold be higher? Or do we slam on the breaks to cross the threshold at Vref?

A lower flap selection will increase your approach speed and landing distance, however in a strong wind on a performance limiting runway the extra wind will reduce your ground speed so depending on type cancel each other out. Good discussion point

As a penalty for learning the answer (D) you can answer this :O

Very Gusty crosswind at 90 degrees to the runway s what flap setting would you select, reduced flap setting makes the runway nearly performance limited, normal flap landing distance is OK. Its an airmanship Q not a performance Q

[PAPI-74]

G-SPOTs Lost -
Good example. Shame the ground school leaves this to the CPL / IR (if the school is a good one).
90 DEG XWC with gusts is git as the GS is almost still air. Normal flap is the way we go, increasing the appraoch speed for the gusts (EDI today was a challange let me tell you) and let the speed reduce in ground effect as you rudder the nose straight while dipping the into wind wing slightly. If there is windshear and turbulance then no messing - 2nd wire firmly making an oooooooaaaahhhhh!!! sound as you land.
Too much flap can give you all sorts of problems, especially without spoilers:eek:

[G-SPOTs Lost]

PAPI - Last bad (red) windshear encounter was at EDI it certainly has its days, its a good discussion point that I got asked when in command training, thinking was in relation to the (more than likely) go around if the x-wind was pushing you towards the terrain then less flap, if you were into wind then more flap.

Great discussion point that leads from x wind landing technique onto OEI go arounds to perf data and where to find it

[PAPI-74]

Indeed -
LCY bit me in the arse on Monday morning. The wind was about 020 17G25 onto rwy10. With this wind direction and rwy, the threshold is sheltered from the wind by an office block on the north dock. With 70deg XWC, mechanical turbulence from the city and then loosing 10 kts from the office block at 30 feet, I didn't have enough in the bank and it ended up a little firm. There should be a sock there to remind us that, although you haven't got a HWC and you had better not be too fast at the threshold, don't forget to keep a bit for the office block windshear.

As you mention G-SPOT, if the ATPL GS was filtered and then updated to include more important information, gaps would most certainly be filled. Certainly in the flight planning / performance / pof / to cover the dangers of these conditions - see youtube. I only really learned about mountain wave when I saw it over the Lake District and during the climb as the VS changed. What is wrong with a few slides and a discussion?
The flight planning / perf was definitely shy of line information. Some argue that this is for the line training, but I beg to differ there. Emergency turns for example and as you mention, OEI perf, using the GPWS / Weather radar as reqd (or at least thinking about it) and where to find the radio failure / emerg descents procedure in the Jep. Probably line stuff, but that is what we are training for not to fill out brains with an example of a pax tripping being covered by the Warsaw Convention. :ugh: And who has the time to learn that as well as the aircraft's systems, limitations, sop's, emergencies, crm, wet drills, FTL's, 1st aid, fire fighting - then off to the sim.
But hey! That is just my opinion.

I hadn't considered less flap for that reason, but makes sence to have less flap. Might be an easier approach too with less flap, giving a smaller crab angle due to the faster approach.

[dartagnan]

you can ad speed in the fms/fmcg (answer A),
or you can ad speed in the FCU by pulling the knob(answer D).

but in anyway, ad speed like half of gust!

[bfisk]

With regards to the crosswind at 90 degrees to the runway; bear in mind the following:

--the wind direction may vary up to but (but not including??) 60 degrees without this being reportable in a metar. A left direct crosswind of 10G20 could veer up to 30 degrees, which would yield a HWC of 5G10, legally without any mention of this in the metar. It could also back bu the same amount, yielding a max TWC of 5G10. Ie total shear in headwind could be .... 10G20!

-- when crabbing on final in a direct crosswind (compared to the runway), the wind is not directly across compared to you, i.e. the gust would have a headwind component.

-- gusts tend to veer compared to the mean wind direction in the northern hemisphere

-- gusts that are the result of showers or mechanical turbulence may just as likely change direction as intensity.

[PAPI-74]

Tell me about it....I need a payrise now you mention it:suspect: