When Vref

[GravityHater]

What were you all taught about when to fly it on approach?
From established inbound?
From final vector to intercept?
From the OM?
From MM inbound? Vref +10 before then?
Does it depend on the aircraft? The company?
Provisios and caveats, too please - including weather variations.

C'mon you can do it.... "I fly Vref from this point inbound ..........."
C'mon you can suppress your natural desire to be rude; "You dumba$$, you have no right to ask such a stupid question!"!

 

[avbug]

Vref is only a reference speed. It's not necessarily a target. Vref is adjusted for weight and weather; gusty conditions dictate an increase, as does increased weight. Approach speeds are typically higher than ref on final, decreasing to Vref over the fence or at touchdown, with touchdown generally taking place at a value somewhat below Vref.


There is nothing magic about Vref itself. It's a starting reference point for determining how one will conduct the approach with respect to airspeed control.

Alternations to normal approach configurations, such as partial flaps, or speed or lift control devices that have been deactivated or are inoperative, play a part in adjustments to the Vref speed. Increments of knots are added for partial flaps, for example, or if the aircraft is carrying ice.

The specifics of the airplane and the approach conditions, and aircraft weight, determine the reference speed. How it is applied also depend on these factors. There is no need to start an approach at reference speed; usually the approach and landing begins at a higher speed, and gradually decreases to a final value that may never be reached until the runway. Sometimes it may be held until the runway as part of a stabilized approach concept.

 

[2000flyer]

I don't think it could have been explained better. Well done AvBug!

Personally, I'll fly most apporoaches around 140KIAS in either the Falcon or Citation. In the Ultra at lighter weights, ref can be as low as 96-98 knots. I would have ATC jumping all over me at larger airports If I spent the last six miles at less than 100 knots, especially if there is a good breeze on my nose. 140 knots works well as I can slow to Vref at the fence comfortably and touch down close to ref. Anything more than 140 on the approach can lead to floating down the runway or having to plant it in the touchdown zone. Again, this is just a personal tip. Our company requires a stabilized approach. Stablized isn't restricted to "ref" as, as AvBug put so well, will vary with conditions.

2000Flyer

 

[Checks]

Army guy, Vref+20 FAF inbound, once visual slowing to Vref over the threshold.

 

[GravityHater]

Succinct and useful info guys (what is happening to this board?!).

One last Q:
Is there anything unsafe with respect to your proximity to the mca by flying for long periods right at Vref, say for the entire approach?

 

[Sphrynxlla]

If i am flying an approach in IMC to near mins. then i will be fully configured by the OM (ils) and fly the glide slope at vref.....if non precision i will keep flaps 20 and ref +10 until i have the field. .......

If i am having fun on a visual, then i will fly final at 160kts down to the MM....dump flaps chop the power and hit ref over the numbers....works out fine. and its more fun.

 

[2000flyer]

One last Q:
Is there anything unsafe with respect to your proximity to the mca by flying for long periods right at Vref, say for the entire approach?

If traffic isn't a problem, you're the PIC and may fly at whatever speed you wish (within regulation of course).

2000Flyer

 

[Guitar Guy]

Actually, Vref has an important function. It is your target speed at 50 feet above the runway, as per FAR Part 1:

Reference landing speed means the speed of the airplane, in a specified landing configuration, at the point where it descends through the 50 foot height in the determination of the landing distance.

And so there's no confusion, here's the definition of Vref from FAR Part 2:

VREF means reference landing speed.

And from FAR Part 25, here are the landing distance calculation regulations (with certain items not related to this discussion removed):

§ 25.125 Landing.
(a) The horizontal distance necessary to land and to come to a complete stop (or to a speed of approximately 3 knots for water landings) from a point 50 feet above the landing surface must be determined (for standard temperatures, at each weight, altitude, and wind within the operational limits established by the applicant for the airplane) as follows:

(1) The airplane must be in the landing configuration.

(2) A stabilized approach, with a calibrated airspeed of VREF, must be maintained down to the 50 foot height. VREF may not be less than

(i) 1.23 VSR0;

(ii) VMCL established under §25.149(f); and

(iii) A speed that provides the maneuvering capability specified in §25.143(g).

(3) Changes in configuration, power or thrust, and speed, must be made in accordance with the established procedures for service operation.

(e) The landing distance data must include correction factors for not more than 50 percent of the nominal wind components along the landing path opposite to the direction of landing, and not less than 150 percent of the nominal wind components along the landing path in the direction of landing.


Note that the FAR's make a point of the importance of being at Vref at 50 feet above the runway. That means that if one has increased his approach speed above Vref for wind gusts, the landing distance will longer than that determined from the airplane flight manual (AFM) unless that speed additive is lost before crossing the 50-foot-above point. It's also important to note that Vref is not an arbitrary number as indicated in FAR Parts 1 and 25. From a manufacturer's standpoint, they want to make Vref as low as possible to reduce landing field length requirements and to help protect against brake energy margins.

As for my current company, our SOP in the Ultra is to fly the final approach segment at Vref + 10 for straight-in approaches and Vref + 20 for circling approaches with Vref being the target speed at 50 feet above the runway. We will bump up the target approach speed (Vref + 10 or 20) for wind gusts but that does not change the target speed over the threshold.

I hope this helps. I've not added anything about abnormal configurations or contaminated runways, but I hope this helps your understanding of Vref and approach speeds. For what it's worth, I was aircraft performance engineer for 11 years before I started flying professionally.

 

[mar]

Airspeed is life

I suppose it all depends on aircraft and conditions *but* when I was a Metroliner capt it would kinda irritate me when copilots would touchdown on a long (10,000') dry runway right at Vref--especially if there was any wind.

Airspeed is life right? Besides that, the Metro controllability is much better with a little extra airspeed.

Now, if the runway was 4,000' long, contaminated with a slight tailwind component, well, now I'm briefing a touchdown at Vref -5.

Know what I mean?

Fly smart.

 

[Sphrynxlla]

yeh... and v ref really has nothing to do with touchdown speed, if you fly an approach at ref..you will always touchdown under ref if you do a normal flare, but i see what you mean. its all the same as long as your vref 50ft hat... except for that stabilized approach thing.

 

[avbug]

Part 25 is a certification regulation, detailing the conditions that must be in effect during the certification process to make certain performance determinations. It in no way contains any regulation, nor does it infer such, that a pilot should operationally maintain any airspeed on final approach.

A pilot is not required to fly Vref, plus or minus Vref, or any other speed, by the regulation. Vref is typically 1.3 times the stalling speed in the landing configuration, or for other configurations, 1.3 times the stalling speed in that particular configuration. That assumes a level stall conducted at the rate of a 1 knot per minute speed decrease, power off.

Vref is different for each aircraft configuration, and each weight.

If you examine your landing performance data for your Ultra, you'll note that you are provided with the exact parameters used to make the landing distance determinations. If you wish that information to be accurate, then you must fly exactly in accordance to those parameters. A few degrees warmer ambient tempeature, a few pounds heavier, a different flap setting, your approach speed higher or lower, and the numbers are no longer accurate. Add to that slight variences in each airframe, bugs on the wing, etc...and the numbers change.

Whereas Part 25 certification for certain demonstration requires showing of a predicted Vref speed at 50 feet, do not assume this provides any requirement what so ever to you or I in operating the aircraft. None. I am not obligated nor required, to fly at Vref. I can fly above it, or below it. If I have gusty conditions, I'll had half the gust factor. If I have ice or am in icing conditions, I may add more speed...or less, depending on the runway condition. I may vary that speed for other traffic in the air or on the runway. I may elect to land with partial flaps or may have a system malfunction that requires it, and my reference speeds will change.

You can fly around all day at Vref, whatever you have determined it to be for your weight and configuration. Won't hurt a thing. But why would you?

Generally you don't want to be below Vref on the approach. So long as you can arrive at the runway without making excursions below Vref, you're okay.

 

[Guitar Guy]

Part 25 is a certification regulation, detailing the conditions that must be in effect during the certification process to make certain performance determinations. It in no way contains any regulation, nor does it infer such, that a pilot should operationally maintain any airspeed on final approach.

I think we may be splitting hairs a bit. While FAR Part 25 may not put an operational requirement on pilots to fly at Vref, consider FAR Parts 121 and 135:

121.195
(a) No person operating a turbine engine powered airplane may take off that airplane at such a weight that (allowing for normal consumption of fuel and oil in flight to the destination or alternate airport) the weight of the airplane on arrival would exceed the landing weight set forth in the Airplane Flight Manual for the elevation of the destination or alternate airport and the ambient temperature anticipated at the time of landing.

135.385 Large transport category airplanes: Turbine engine powered: Landing limitations: Destination airports.
(a) No person operating a turbine engine powered large transport category airplane may take off that airplane at a weight that (allowing for normal consumption of fuel and oil in flight to the destination or alternate airport) the weight of the airplane on arrival would exceed the landing weight in the Airplane Flight Manual for the elevation of the destination or alternate airport and the ambient temperature anticipated at the time of landing.

If one is intending to land on a short runway, very near the AFM-determined runway length requirement, being above Vref at 50 feet over the runway would invalidate the landing field length requirement determined from the AFM and one would have to have some sort of valid data to support the speed over the threshold in order to not violate the appropriate requirement in FAR 121 or 135. The information that I've seen in the Ultra AFM very clearly spells out the requirement for Vref at 50 feet.

 

[Bandit60]

I suppose it all depends on aircraft and conditions *but* when I was a Metroliner capt it would kinda irritate me when copilots would touchdown on a long (10,000') dry runway right at Vref--especially if there was any wind.

Airspeed is life right? Besides that, the Metro controllability is much better with a little extra airspeed.

Now, if the runway was 4,000' long, contaminated with a slight tailwind component, well, now I'm briefing a touchdown at Vref -5.

Know what I mean?

Fly smart.

This could be a dangerous statement. On higher performance airplanes that have higher ref speeds (Lear55-60 for example), this could cause you to get into alot of trouble.
1. your landing distance if over ref speed is expedential (spelling?). A few nots faster could add alot of landing distance for your airplane. In this case speed can kill.

2. You also be come a test pilot for your situation...break energy clould be a huge factor and so can wheel speed.

 

[avbug]

Brake energy, not break energy.

Increased energy with increased velocity is exponential, but adding extra speed to one's approach does not equate to touchdown speed, nor necessarily increased runway distance.

If one is attempting to shoehorn an airplane into the lower ragged edge of it's stopping capability, one is facing a judgement issue, not a performance issue. If one is unable to add extra speed because the airplane has the bare minimum stopping distance, one needs to be considering a different field, a lesser weight, or a better day.

121.195 and 135.385 refer to takeoff limitations; these regulations speak to launching a flight, not terminating it. In other words, the distance in which one actually stops isn't relevant to the regulation. The regulation speaks to preflight planning and dispatch. You can't leave unless the performance charts indicate that you fall within the specified parameters. If you arrive with extra fuel, fly faster, have a system malfunction, use partial flaps, carry ice, encounter turbulence and gusty conditions, or any other reason for carrying extra speed and using extra landing distance, these have no bearing on 121.195 or 135.385.

These regulations only mean you can't launch if your predicted performance does not fall within the specified parameters. Real world performance, or in other words, what actually occurs when you get there, is irrelevant to the regulation. The regulation does not stipulate that you cannot use more distance; only that you can't plan on using more distance. You can use the entire runway on arrival, if you wish. I often do. I don't like braking any more than I need to, and if opportunity exists, I will always let the airplane roll out.

I still need to be capable at the time of takeoff, based on anticipated and forecast fuel burn and conditions, to show that I could stop in a given distance, but there is NO requirement to stop within that distance when I get there. The requirements of 121.195 and 135.385 end when the aircraft takes off.

 

[typhoonpilot]

That assumes a level stall conducted at the rate of a 1 knot per minute speed decrease, power off.

I know you meant one knot per second, or are the test guys trying to build flight time .

To answer the original question, it is all a matter of practicality. In the real world nobody is flying Vref from the Final Approach Fix inbound in anything other than a simulator. In that case, in transport category aircraft, the speed is Vref plus 5 as a minimum and Vref plus additives for wind ( speed and/or gust ) up to a maximum of Vref plus 20. That speed is held all the way down to 50 feet or whenever the autothrottles on your particalur aircraft start to retard.

At a fair number of the big international airports they request that you maintain 160 to a 4 mile final. For heavy jets that isn't too far away from the final approach speed, but it would be well above for turboprops, etc.

As a general rule I lke to be fully configured and on speed by 1000 feet AAL in IMC conditions and 500 feet AAL in VMC conditions. If flying a Category II approach or higher than it would be by 1500 feet. My company has recently imposed a rule that we must be stabilized by 1000 feet, even in VMC. That is a safer rule and I abide by it, although I sometimes miss the days of flying the MD-80 in Taiwan when I maintained 320 to a 15 mile final .


Typhoonpilot

 

[avbug]

1 knot per second. A minute might be a tad overkill.

 

[mar]

Yes and no.

This could be a dangerous statement...In this case speed can kill...You also be come a test pilot for your situation...

Well, like I said, it depends, doesn't it?

And like Avbug said, there are two issues: judgement and performance. That's why we get paid the big bucks to operate really expensive modern equipment packed with lovely flight attendents and very important cargo.

Or not.

Fly smart.

 

[Bandit60]

I do agree with you and sorry about break instead of brake. (brain fart)