Landing above Vref

[Night Flight]

Hi All,

Is anyone familiar with a rule of thumb for calculating landing distance when landing above Vref. We use Vref+5 as a company SOP and as most can use up to Vref+10 in gusty conditions. We can also use Vref+20 if landing with an anti-icing failure (althought the manufacturer provides guidance for this to add 50% to the LDR).

How would this vary for a dry and wet runway?

What about aircraft size?

If I wanted to calculate the actual LDR for a higher Vref rather than just using a rule of thumb, is there a technique for this?

Thanks in advance.

NF

[Intruder]

Does your FCOM or QRH or Performance Handbook not have appropriate charts or tables? Our 744 QRH has a table that has that specific information (410-750' per 10 KT above Vref, depending on Flap configuration, Autobrake setting, and runway condition).

[john_tullamarine]

Providing you can keep the float under some sort of reasonable control, distance ratio will approximate the ratio of the speeds squared.

[safetypee]

Landing distance should be corrected for any speed increment above Vref, which is planned or expected at the threshold. Most manufacturers provide corrected distances for failures / abnormal configuration, icing, and may also provide correction for thrust reverse, brake setting, and speed excess.

A general rule of thumb for speed excess is 300 ft per 10 kts on a dry runway and 500 ft per 10 kts on a wet runway ( AC 91 79 Runway Overrun Prevention (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%2091-79/$FILE/AC_91_79.pdf)).
However as JT states, providing you can avoid floating which might be more difficult with increased speed.
The distance penalty for floating is very high; 2500 ft per 10kts; also or alternatively consider any delay in touchdown; 230 ft per sec.
So a simple 10 kts excess could easily add an extra 3000 ft to the actual landing distance.

[OPEN DES]

Rule of thumb: 10% extra LDR for every 5kt. A bit conservative but works.

[Intruder]

A couple of notes just for discussion:

Note that the rule of thumb cited by Safetypee is NOT conservative when applied to the 747. That illustrates the dangers in relying on rules of thumb when more accurate data are available.

Float is generally accompanied by deceleration, unless the pilot is REALLY gooning it and forgets to reduce thrust. So even though the float itself adds significant stopping distance before touchdown, I don't think the [relatively minor] would be stopping distance once on the ground would be additive.

[IcePack]

200 ft per knot works for me. Told to me 30+ yrs ago. i.e inc a bit of float & the extra brake dist. But yep not to be taken as a definitive distance.

[bubbers44]

Landing at TGU Honduras in a B757 I used the 1,000 ft mark of runway remaining as what I should land in and always did over 600 times. That means I would have landed in 4,000 ft on a 3300 elevation strip all of the time. We always landed at ref plus 5. We never needed that last 1,000 ft of a 5400 ft runway. Just fly a stabilized approach and all will be fine.