737-700 landing distance

[Allan]

Standard zero wind approach speed is Vref+5. This is held until retarding thrust levers to flare. If you want to know your landing distance on a dry runway, you enter QRH, PI 12.1. You find e.g. 790 meters for a dry runway, max manual braking, flaps are 40 according to notes on bottom. In table below you have adjustments for the landing distance. My question is: Should you make adjustmens to the landing distance because you approach with Vref+5 and the adjustment-table states "approach speed" "per 10 kts above Vref" or is the table based on you flying Vref+5 and hence no adjustment is necessary? If the latter is the case, what if you fly with Vref+20 due to gust?

[Flight Detent]

Hi Allan,

My PI (?) states quite clearly that the adjustments are;

"Based on flaps 40, VREF40 approach speed"

To me, anything different is an adjustment!

Cheers

[Stephen]

It depends on the circumstances whether you should make adjustments to the landing distance because you approach with Vref+x kts.

The Boeing Flight Crew Training Manual (FCTM) 1.22 (Command Speed - Landing) and 6.9 (Landing - Flare and Touchdown) says that you should land with an airspeed of approximately Vref + GUST correction. This means that when you approach touchdown, you should bleed off the correction for the STEADY headwind component (HWC), while maintaining the gust correction.
Therefore, for determination of your landing distance, you may disregard the corrections on Vref for the STEADY headwind component, while taking into account the corrections for the gust.

Example I:
landing runway 23
W/V = 230/16, no gusts reported
FAS = Vref40 + WCF
= Vref40 + 0.5*HWC + gust
= Vref40 + 0.5*16
= Vref40 + 8

According to the FCTM, you will approach touchdown with a speed of Vref40: the steady wind correction does not have to be taken into account when determining the Vref-adjustment, as the 8 kts steady wind correction should be bled off as you approach touchdown.

Example II
landing runway 23
W/V = 230/16G28
FAS = Vref40 + WCF
= Vref40 + 0.5*HWC + gust
= Vref40 + 0.5*16 + 12
= Vref40 + 8 + 12
= Vref40 + 20
According to the FCTM, you will approach touchdown with a speed of Vref40+12. The 8 kts correction for the steady HWC shall be bled off, but the 12 kts correction for the gust shall be maintained until touchdown. You should only apply the gust correction of 12 kts on Vref40, so use a landing distance adjustment for 12 kts above Vref.

Regards,
Stephen