Simple question regarding Vref and Vref + Factor

calcapt said:
Remember guys that Vref is calculated on a given weight. I absolutely guarantee that the airplane does not weigh exactly what the Vref numbers are predicated on. On a 737-900 with 170 people onboard I would guess the actual weight of the airplane could be off by several thousand pounds either way based on the actual weight of your passengers and cargo. For those of you who do not know, airlines calculate average weights for passengers and bags. If you happen to be flying a bunch of skinny people, your actual weight may be far less than the weight your performance is based on; conversely, if you are carrying a bunch of sumo wrestlers, your actual weight might be thousands of pounds heavier than the weight you are using to determine Vref. That would explain why a particular aircraft might fly great at Vref one day and feel sluggish and a bit slow on another day. I will take my Vref +5 as a little insurance for how fat America has become. Just my 2 cents.....
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What percentage you all talking about?
(#lbs the aircraft could reasonably be off at MTOW / MTOW) * 100= %
My weight card I expect it to be off by THIS much at most:
Saab 340 - 2%
CRJ 2?
CRJ 9?
737?
717?
MD11?

Knots that would make you off by:
Saab 340 - 1-2knots
CRJ 2?
CRJ 9?
737?
717?
MD11?

In the old Saab-o-matic I don't see 2% as a big deal honestly. Just go by what the card says and it'll be a whole knot diff.
 
You're making the assumption that everyone in the back weighs 195 lbs and that every checked bag weighs 30 lbs in order to get your weight that you're using to read the cards, these assumptions combined with the 2-3% difference in between cards could amount to a significent difference.
 
True, but I know at our airline, if the landing weight is, say 45,100 lbs, we set the speeds for 46,000. So you're already compensating right there.

Also, for every 250 lb guy on the plane, I'm betting there's a good chance of a 130 lb girl to offset his weight. Well, maybe not flying outta MSP. :)
 
SpiraMirabilis said:
You're making the assumption that everyone in the back weighs 195 lbs and that every checked bag weighs 30 lbs in order to get your weight that you're using to read the cards, these assumptions combined with the 2-3% difference in between cards could amount to a significent difference.
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No.

What I'm saying is between the people getting on weighing differently AND their bags no being the precise weight that I feel the most the planes weight will be off from our calculations is about 500lbs. I'm a 2 year rampie at JFK and EWR and weight and balance officer for 24 different airlines for everything from a A310 to a MD 11 and a 747. I've been board during loading and watched the back and I feel that the most we are off (reasonably) is about 500 pounds with a saab 340. thats about 2%. If it happens right at the point where we flip the card it makes about 1-2 knot diff on Vref.

So I'm curious if some of the other guys flying the types I listed on this thread could throw out a couple of their own ideas on how much in % and knot diff in Vref they think they are at worst (reasonably).
 
Interesting-ish discussion.

We have a general question answered by folks that fly all types of airplanes. Then there are retorts that the people who fly different airplanes are wrong.

Then it gets into what the meat of the issue is. A theoretical, or planning purposes, number which is used as a baseline to establish aircraft performance for landing. Then the idea comes up that there are other factors influencing the performance.

In a perfect world, no wind, no wind gusts, perfect pilots and all, once crosses the threshold at 50', continues on a 3* glide, lands uses brakes and stops in X distance. However, the world isn't perfect, and we don't fly perfect.

Some airplanes, specifically the E170 is FAA authorized to land with the autothrottles on. The target speed, a minimum of Vref+5, is flown until the power comes off at 30'. That is the way the machine works, and was approved to work by the FAA during certification.

There are reasons that you have additives for your performance numbers. Everytime you have an abnormal that will affect the stopping distance, you get a correction. In every plane I've been trained in, you don't fly at Vref. You fly at Vref+any additive you add until you flare. Some airplanes may be differnt, and that's OK.

Fly it how you were trainined and within your company's procedures. There's a good chance that the people that wrote the procedures knew what they were doing.
 
I'm gonna toss in another here. I, and many others in the Q fly a deck angle, and note the refrence to the speeds. If you hold power to maintain a +2deg deck angle(flaps 15) on glide slope, then you will normally cross 50ft at red+5 to 10. At that point the airplane will land with almost no flare by the pilot. 5deg is our pitch limit, so we really depend on ground effect to flare us, not pitch changes. The first time u do it, it will scare you.
 
Polar742 said:
Fly it how you were trainined and within your company's procedures. There's a good chance that the people that wrote the procedures knew what they were doing.
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I don't believe that here. We were flying Vref+5, then suddenly we're flying Vref with no explanation other than a plane went off the end of the runway.

Most of our procedure changes seem to be knee jerk reactions with no thought. Like "Have a new checklist" then, when we get on the line, we realize the new checklists don't work with things like APU deferred. Instead of correcting the mistake or issuing a revision, the company says "Uh.....just use the old one, or something." They basically INVITE making up your own stuff. Not good.
 
surreal1221 said:
What do PTS have to do with this? ;)

Oh I think I get it. . .if a pilot can satisfy checkride requirements, surely they wouldn't allow airspeed to decay below Vref minus 5kts.

Is that it? ;)

Or. . .Since most companies recommend Vref+5, the ATP standards of +/- 5kts would, on the minus side of things, allow the speed to still be at Vref if the pilot was flying to ATP standards.

Is that it?
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Nope, there is a reason the "bug" is +/- 5 knots (10 kt total coverage). I forget the ATP standards but I thought they were +/- 5 but could be wrong. Nobody is perfect and there are many environmental and mechanical variables that results in the published Vref being 30% higher than the calculated stall speed.
 
I don't know how you guys do it over at PCL, but they teach us to set the speed bug to our Vref+5 speed, and to set Vref as it is from the speed cards or ACARS data. So, by going below the bucket we are going under Vref. At the top of the bucket is Vref+10.
 
surreal1221 said:
I don't know how you guys do it over at PCL, but they teach us to set the speed bug to our Vref+5 speed, and to set Vref as it is from the speed cards or ACARS data. So, by going below the bucket we are going under Vref. At the top of the bucket is Vref+10.
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We bug Vref from the speed cards. So, top of the bug is Vref +5. How do you set the speed bug to Vref +5 AND set Vref from the speed card? The only presets I know of are V1, Vr, V2 and VT. V2 and VT are bugged for a go around with us.

Edit: I think I get it. You get the Vref from the card (thus setting it) and then just bug Vref +5. That's how we used to do it up until TVC.
 
We have little plastic things that you can roll around the outside of the airspeed indicator but they dont really work so well. A lot easier to just remember what your ref is and keep your scan on the speed barrel.
 
What surreal is saying is that they (ASA) use the Vr bug and bug Vref with that, then use the speed bug "bucket" to bug their target speed down final.

Makes much more sense to me...Pinnacle has always had a way of doing knee jerk, nonsensical reactions to things that take years (and more issues) to correct.

Sounds like the TSA.....
 
PeanuckleCRJ said:
What surreal is saying is that they (ASA) use the Vr bug and bug Vref with that, then use the speed bug "bucket" to bug their target speed down final.
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There was an informal procedure of doing that here as well. The nice thing about it was once you had the Vr bugline set to your Vref speed all you had to do was drop the bottom of the actual speed bug down to the Vr line and you had just bugged Ref+5.

However, we had two checkairmen who violently opposed the idea because they said in the event of a single engine go around (which we all know happens SO often) there would be too many lines on the speed tape and the ONLY thing there should be Vt.

Apparently they won out because I haven't seen anybody do that in a long time.

As far as flying the ref speed... If I recall (and I can't find any paperwork to back this up) the published VRef speeds in the book for the CRJ as significently higher than they have to be (somewhere around 1.27 to 1.30 Vso) because of the super critical wing and no leading edge devices. Early on in the operations of the airplane +5 was used (just like most other airplanes) but apparently that +5 was already factored into the actual Ref speed to begin with so flying +5 is actually more like flying +10. As far as I know, 9E is the only company to stop flying at +5, but then again, they are the only one to have had a -200 go off the end. Everybody else who has put one in the dirt has done it off the side.
 
BobDDuck said:
However, we had two checkairmen who violently opposed the idea because they said in the event of a single engine go around (which we all know happens SO often) there would be too many lines on the speed tape and the ONLY thing there should be Vt.
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So, if the go around and engine failure happened below 1000 AGL....what would they bug? Shouldn't V2 be set as well?

I just don't see too much benefit in setting the Vr bug for Vref if you've already got the speed bug. Even if you set Vref +5, you know Vref is the bottom of the speed bug.
 
Vref to Vref + 10 over the fence for the Brasilia. On a normal day, I usually add about 5 knots to Vref. Shorter runways like Sun Valley or St. George, then I like to be at Vref.
 
I tried coming in at Vref as opposed to Vref+5 at 50 feet and felt like that plane wanted to fall out of the sky:D
 
Polar742 said:
Interesting-ish discussion.

We have a general question answered by folks that fly all types of airplanes. Then there are retorts that the people who fly different airplanes are wrong.

Then it gets into what the meat of the issue is. A theoretical, or planning purposes, number which is used as a baseline to establish aircraft performance for landing. Then the idea comes up that there are other factors influencing the performance.

In a perfect world, no wind, no wind gusts, perfect pilots and all, once crosses the threshold at 50', continues on a 3* glide, lands uses brakes and stops in X distance. However, the world isn't perfect, and we don't fly perfect.

Some airplanes, specifically the E170 is FAA authorized to land with the autothrottles on. The target speed, a minimum of Vref+5, is flown until the power comes off at 30'. That is the way the machine works, and was approved to work by the FAA during certification.

There are reasons that you have additives for your performance numbers. Everytime you have an abnormal that will affect the stopping distance, you get a correction. In every plane I've been trained in, you don't fly at Vref. You fly at Vref+any additive you add until you flare. Some airplanes may be differnt, and that's OK.

Fly it how you were trainined and within your company's procedures. There's a good chance that the people that wrote the procedures knew what they were doing.
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True dat. Here's how it was explained to me by a check airman on IOE on the -145.

Fly target (VREF+5) on the approach, plus whatever other numbers you're flying. You've flown the thing, and I'm sure you guys did the same thing at CHQ, but if your target number is sitting in the white arc, bump it up 5 knots.

When you're in the last 100' of the approach, lose those 5 knots. I would generally try to keep the plane at VREF until I'm just settling into the flare, and would close the throttles slowly throughout the last 50' or so of the approach, but of course that's considering a no wind day that's smooth as glass.

I've had days where I've rolled it on with the above technique, and I've had days when I had carrier style landings (runway 33 at DCA) and had the thing stopped within 2,500'. In the end, I always thought the approach of making the numbers do what you need them to do worked best, or in other words; don't forget that you're paid to be a pilot, not a machine (in most cases). If the numbers need to get tweaked a knot or two up or down because of conditions, by all means do it. I've also found listening to the techniques from the various guys that sat to the left of me helped a lot. Not all of their techniques worked all of the time, but they could give you a lot of guidance depending on the situation.
 
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