Simple question regarding Vref and Vref + Factor

[Rocketman99]

Let me take that a little further with some examples taken from the KC-135 (B707) and the Saab. In the mighty tanker, you planned to cross the runway threshold speed at Vth which is the equivalent of Vref and then touchdown at TH -10 or ref -10. Vth was
calculated based on 50 degrees of flaps. So Vth=Vref=Vapp for 50 flaps. Touchdown speed was Vth -10 kts. Now corrections were made for gusty winds for the gust factor, so if the winds where whatever at 25 gusting to 35, you added 10 kts to the ref speed.

In the equally mighty Saab, there were no such distinctions made about touchdown speed, but the landing data charts assume crossing the threshold at 50 ft at flight idle and a speed of Vref.

Lastly, in the large piece of canadian crap Q400, the landing data charts are also all predicated on a speed of Vref.

I'm NOT advocating going against company policy or flight manual procedures per se. I'm just saying make sure you know what your landing data is based on. Airspeed is life, but too much airspeed can be just as detrimental.

Food for thought.

 

[jtrain609]

Yeah, but you're (mostly) all advocating flying faster than you need to/are supposed to. That's the problem. OK so ref +5 isn't a big deal. Ok, so you're shooting for that but now you're flying ref +10 or 20 trying to correct to it. That's where the problem is. Fact of the matter is, you're not even remotely close to falling out of the sky at ref. What, it's 1.3 times stall speed or so. Even with a gust you're not remotely close to falling out of the sky at ref, so you're advocating flying fast for no reason. Now if your company's procedures/told data tell you otherwise great. However, if you're adding extra speed for mom and apple pie you're hurting rather than helping yourself, especially in adverse conditions. Seems like people tend to forget that ref speed already gives you a HUGE cushion above stall speed. Short of flying into a hurricane you would never be close to a stall flying AT ref.

So like I said, you fly the numbers the book tells you to, you stop on the runway, you go to the overnight.

I mean, this doesn't seem like rocket science ya know? I mean don't get me wrong, I had one hell of a night going into ALB one night and we landed at some ungodly speed that according to everybody here would have meant cats and dogs living with each other (the book said we'd be fine), but we still stopped on west bound runway at ALB in what was easily the most turbulent approach of my life.

I dunno guys, it just doesn't seem that complicated. Fly the airplane, use the numbers, make the numbers work for you and if you don't like where things are going then go around.

 

[SlumTodd_Millionaire]

For those that think 5 knots isn't a big deal, I beg to differ. Every knot of airspeed results in roughly an addition 100 feet of landing distance for the average transport category aircraft. I tend to think of 500 feet of runway being a significant difference. Now, let's say your airspeed control is at the limits of ATP standards, and you're holding target airspeed +5 knots. Now you're technically 10 knots over the speed calculated in the manual for landing data, or 1,000 feet extra on the landing distance. Now, let's take it a step further and say that your airspeed control isn't quite up to ATP standards, because let's face it, we get all get a tad bit sloppy at times. So let's say that your airspeed control is crappy, and you're crossing threshold at target speed +10. If you were using Vref +5 as your target threshold crossing speed (incorrectly, I might add), then you're now at 15 knots over calculated threshold crossing speed. That's an additional 1,500 feet of landing distance over book numbers. The use of thrust reversers obviously mitigates that, since most book numbers are predicated only upon brake usage, but it's still a significant number.

Don't scoff at a few knots. A few knots can become a big deal. I'm not saying that anyone should be the jerk that constantly says "airspeed" whenever the PF is 6 knots off the bug, but I am saying that you shouldn't allow yourself to get sloppy "because it's just a few knots." If your manual says to cross the threshold at Vref, then you should strive to do that. Don't accept Vref +5 just because it's easier, or just because it's only a few knots. Anyone ever read Fate is the Hunter? The last time I read it was about a year ago, but if memory serves, the prologue is his discussion about how he almost slammed into another plane in the middle of the night, and that if he had been a tiny bit sloppy and been just 100 feet off his assigned altitude, he would have hit that other plane. Sloppiness kills, folks. Fly the manual.

 

[derg]

And if you fly it at Vref instead of Vref+5, you won't fall out of the sky. I've done it 7 times this week. I didn't even get the shaker.

Don't do that in a mad dog!

 

[EDUC8-or]

For those that think 5 knots isn't a big deal, I beg to differ. Every knot of airspeed results in roughly an addition 100 feet of landing distance for the average transport category aircraft. I tend to think of 500 feet of runway being a significant difference. Now, let's say your airspeed control is at the limits of ATP standards, and you're holding target airspeed +5 knots. Now you're technically 10 knots over the speed calculated in the manual for landing data, or 1,000 feet extra on the landing distance. Now, let's take it a step further and say that your airspeed control isn't quite up to ATP standards, because let's face it, we get all get a tad bit sloppy at times. So let's say that your airspeed control is crappy, and you're crossing threshold at target speed +10. If you were using Vref +5 as your target threshold crossing speed (incorrectly, I might add), then you're now at 15 knots over calculated threshold crossing speed. That's an additional 1,500 feet of landing distance over book numbers. The use of thrust reversers obviously mitigates that, since most book numbers are predicated only upon brake usage, but it's still a significant number.

Don't scoff at a few knots. A few knots can become a big deal. I'm not saying that anyone should be the jerk that constantly says "airspeed" whenever the PF is 6 knots off the bug, but I am saying that you shouldn't allow yourself to get sloppy "because it's just a few knots." If your manual says to cross the threshold at Vref, then you should strive to do that. Don't accept Vref +5 just because it's easier, or just because it's only a few knots. Anyone ever read Fate is the Hunter? The last time I read it was about a year ago, but if memory serves, the prologue is his discussion about how he almost slammed into another plane in the middle of the night, and that if he had been a tiny bit sloppy and been just 100 feet off his assigned altitude, he would have hit that other plane. Sloppiness kills, folks. Fly the manual.

I'm not sure where you're getting your numbers, if you check the advisory circular it's closer to 300' per 10 knots on a dry runway and 500' per 10 knots on a wet runway.

Also, you're making a blanket statement that ref+5 to touchdown is incorrect. Different airplanes and companies require different procedures.

 

[fish314]

I'm not sure where you're getting your numbers, if you check the advisory circular it's closer to 300' per 5 knots on a dry runway and 500' per 5 knots on a wet runway.

Also, you're making a blanket statement that ref+5 to touchdown is incorrect. Different airplanes and companies require different procedures.

If that's the case, then the 100' per knot is a pretty good round number approximation. It's about spot on in the case of a wet runway, and a little conservative in its estimate on a dry one.

As for the blanket statement about touchdown being ref+5, and different companies and different aircraft requiring different procedures, I think that's a valid point. But I think the question that the thread was trying to address is whether you or your company advocate a speed that is greater than the speed in the "book" (whatever that speed happens to be, or to be called). So basically, whatever your aircraft's performance numbers are based on (whether it's 50 at Vref and throttles at IDLE, or 50' at Vref but throttles NOT at IDLe, or 50' at Vref+5, etc., etc.,) do you PLAN to fly faster than THAT? Maybe the best way to ask the question, instead of using Vref or Vth, or Vapp, would be do you fly "Book", or "Book + something".

PCL's point still seems valid to me. If you are planning on flying a speed that is ALREADY artificially increased by 5 knots, and you fly it a little fast due to proficiency/ability, it can result in an increase in landing roll that falls outside of what most folks would consider "insignificant".

 

[EDUC8-or]

The AC actually states 300' per 10 knots dry and 500' per 10 knots wet, that's where I noticed the discrepancy between 1 knot and 100', I edited my previous post to reflect that information. I think it's time for a cup of coffee.

I stand by what I said about the blanket statement. He's saying if your're crossing the threshold at ref+5 you're doing it wrong. That's the way we train at our company and that's the way our landing data is calculated. Could we transition to ref at the threshold? Absolutely, and we fly an airplane that wouldn't bite you in the you know what if you do, but there are several out there that might.

 

[SlumTodd_Millionaire]

The AC actually states 300' per 10 knots dry and 500' per 10 knots wet, that's where I noticed the discrepancy between 1 knot and 100', I edited my previous post to reflect that information. I think it's time for a cup of coffee.

I was going off of memory based on what's in those fancy books that you have to read to prepare for Cathay and Delta interviews. My memory may be wrong. In any case, extra runway is extra runway.

I stand by what I said about the blanket statement. He's saying if your're crossing the threshold at ref+5 you're doing it wrong.

I'm not saying that at all. Go back and look. I'm saying "fly the manual." If your manual doesn't say to do it that way, then do it the way your manual says. On the 717, the autothrottles stay connected the whole time, so you don't manage your airspeed to reduce to Vref at the threshold anyway, so it's obviously not universal. On the CRJ, though, we were trained for Vref at the threshold. Whatever your manuals state, that's what you should be doing.

 

[fish314]

I'm not saying that at all. Go back and look. I'm saying "fly the manual." If your manual doesn't say to do it that way, then do it the way your manual says. On the 717, the autothrottles stay connected the whole time, so you don't manage your airspeed to reduce to Vref at the threshold anyway, so it's obviously not universal. On the CRJ, though, we were trained for Vref at the threshold. Whatever your manuals state, that's what you should be doing.

:yeahthat: Fly the way the book says to fly it.


That said, I understand crossing fast in certain situations. Like, you are a CFI in a C172, and your student is having trouble landing. Your computed distance is 1000' and you are flying into a 7000' field. You could cross 10, 15, or maybe even 20 fast with no problems, and you need to just to be able to get any training done at all. But you've taken that into account by going to a field where you're not even close to worrying about landing distance.

Or, you are an aerobatics pilot doing an airshow, and for your next trick you are going to come down 10 feet over the runway, go into inverted flight over the runway, then at mid-field flip back over right side up and land at show center. Your threshold crossing speed in THAT scenario might be ref+100. But you can bet that the airshow pilot has taken every portion of that maneuver into account.

Or, you had a mid-air, and half of your left wing is missing. You need 30 extra knots to maintain controllability. You've limped it over to the longest field you can, and you need to land....NOW.

Or, you are a test pilot, and the book hasn't been written yet.

Any of these scenarios, and probably a whole lot of others, justify modifying the procedures and not following the book... but they are the exceptions, not the rule. In general practice, you should fly as close as you are able to fly the way the book says to fly. If there is a good reason where what the book says shouldn't be the general practice, then you should work to get the book changed.

 

[Polar742]

Starting with rocketman's post 102 and on down, I don't think anyone on this thread was arguing those points.

The question asked was if you fly Vref or Vref + factor. It wasn't do you fly Vref or Vref+your personal additive.

The bend came when people pointed out that airplanes, small (RJ) or big (747), tend to fly an approach at Vref+a derived target speed. As are all things in aviation, some operators prefer a pure Vref speed, and that's OK.

The bone of contention was when some said it's wrong to fly any speed above Vref, and that's incorrect. Again, all BASELINE performance is derived off of Vref, as there has to be a constant. There are performance corrections on the planes I flew for non-standard (greater than Vref+5) target speeds, to adjust for the landing data. Some airplanes have landing data correction for target speeds above a certain range (think Vref+10).

You can verify this in a simple manner by looking at your QRH for a no-flap landing. It will typically give a derived Vref speed + and additive for the bad juju. Then there will be a mulitplier for the landing distance.

And don't forget, your landing performance is predicated on a certain type of braking. Make sure you get up on the binders too, unless you have autobrakes with appropriate performance.:crazy: Because you can touchdown on the fixed distance markers at Vref to Vref-5, and if you don't brake according to your perfomance manual, you'll just blow all your landing performance numbers out of the water.

I guess there is a reason the FAA has the 60% rule since I'm not a perfect pilot.

 

[kellwolf]

Also, you're making a blanket statement that ref+5 to touchdown is incorrect. Different airplanes and companies require different procedures.

Agree. The CRJ is a float machine. I've found that if you're flying Vref instead of Vref + 5, you're fighting the float a LOT less. Your other option is to plant it. I struggled with landing it within company landing standards (first 1500' of runway) when we were flying Vref+5 and NOT floating or planting. When we went to flying Vref, it got a LOT easier to land without floating. If the POS airplane had slats like the -700 or the -900, I doubt floating would be an issue. As it is, if you pitch the nose up 2-3 degrees more than you need, you're along for the ride.

Just looked at the contaminated landing charts for us, and it says add 70 ft of runway for each kt above Vref. So, if you're flying Vref+5....that's an extra 350 feet. 350 feet shorter, and our TVC flight would just been "Oh, man. We ALMOST ran off the runway" instead of on the news.

 

[SmitteyB]

I'm really not understanding how anyone can say Vref is dangerously slow given how the number is calculated by manufactuers.

If Vref is dangerously slow, what is Vso? Insanely Slow?

I'm saying REF-10/15 is a slow touchdown speed.

Flying the approach at REF in my opinion is slow.

 

[jynxyjoe]

I'm saying REF-10/15 is a slow touchdown speed.

Flying the approach at REF in my opinion is slow.

Try that lever looking thing on your far left next time (push forward slowly). Works wonders on that speed for touchdown. Not being entirely serious here.

Honestly I'll take a look next time I'm touching down, REF -10/15 sounds fine by me (110 on light days minus 15 is 95'ish). The guys at Mesaba brought this up because of guys from the AVRO believing you have to touch down at ref (that's how it was explained to me don't ask me to explain, I'm just a saab captain): "You are suppose to be below ref touching down." Maybe there is a bent a** airplane or two that doesn't fly well below ref, some of them fly like crap above ref, but having the opinion the thing doesn't fly right at 10-15 below ref inches about the ground is a little new to me.

 

[kellwolf]

Flying the approach at REF in my opinion is slow.

Yeah, I still don't fall out of the sky at Vref on the approach. At the higher weights, we won't even see the low speed cue on the PFD. Call me crazy, but 142 kts isn't really "slow."

 

[zmiller4]

Honestly I'll take a look next time I'm touching down, REF -10/15 sounds fine by me (110 on light days minus 15 is 95'ish).

That's an interesting point, actually. On my aircraft checkout in the ATR I got chewed out by the captain (not the examiner, who was in the JS) for "touching down below Vref". Funny thing is, though, that the ATR had a basically flat pitch at Vref, so if you touched down at that you had a good chance of a super-flat pre-solo-student landing. I was confused and had to call my instructor, who backed me up.

 

[jynxyjoe]

I had a few Capt's on the beech 1900 at CJC that had a horn go off on landing a few times. Two of them were check airmen. I didn't think too much of it (cause I was a low time, useless, unexperienced FO) until a captain told me that was no bueno. Obviously that won't transfer over to the jet's very well, but turboprops don't get real finicky under "ref" from what I've seen. ATR/Q guys please chime in.

 

[jtrain609]

Does it matter if it doesn't transfer over to jets very well?

I landed Cessna 172's in a full stall, and attempted to avoid it in the Chieftain (I figured if the stall horn chirped as the mains touched down I had done my job correctly), didn't even consider it in the EMB-145 and now...well now I fly a pair of ski's so I guess ref speed doesn't mean much to me.

Point being, though, and I think this might be the theme of the entire thread; just fly the God damned airplane. If it's designed to be landed in a full stall (I don't know anything about the B1900 to be frank, I've got a few hours in the Beech 99 but don't remember a ton about it other than I loved it) then land it in a full stall, but don't avoid flying the plane properly because those skills won't transfer properly to another airplane.

I know I've probably just completely derailed your thought process, but I figured I'd just point that out

 

[jynxyjoe]

I know I've probably just completely derailed your thought process

What? Dave's not here man.

 

[jtrain609]

 

[Rocketman99]

No man, I'm Dave. Come on man let me in.