767-300 Vref Question
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767-300 Vref Question
One for the 763 drivers, why are Vref30 and Vref25 the same speed at around 160,000kg on the 767-300, and at higher weights than this why is Vref25 lower than Vref30?
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Re: 767-300 Vref Question
This is because Flap 30 and therefore Vref30 is not used for landing above about 160,000kg. The Flight Manual states that when the Vref30 is within 10 kts of the Flap 30 placard speed (170kts) Flap 25 should be used for landing.
The -300 has the same wing as the -200 but is considerably heavier (roughly 186,000kg MTOW instead of 156,000kg). Boeing found that at min clean speed, Vref30+80, the lift margin on the -300 at max weight was a bit tight, so by increasing the Vref30 at high weights they are increasing the manoeuvring speeds. This higher Vref is not used for landing; if you had to land at these weights you would use Flap 25.
It can make the departure quite complicated though as the minimum manoeuvring speed can exceed the flap placard speed, eg +80 is 256kts but 250kts is max speed until the flap is up.
The -300 has the same wing as the -200 but is considerably heavier (roughly 186,000kg MTOW instead of 156,000kg). Boeing found that at min clean speed, Vref30+80, the lift margin on the -300 at max weight was a bit tight, so by increasing the Vref30 at high weights they are increasing the manoeuvring speeds. This higher Vref is not used for landing; if you had to land at these weights you would use Flap 25.
It can make the departure quite complicated though as the minimum manoeuvring speed can exceed the flap placard speed, eg +80 is 256kts but 250kts is max speed until the flap is up.
Last edited by Silvershadow; 9th Jan 2006 at 08:44.
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Also the Flap speeds are based on Vref30. I believe these would be too low at some weights if based on the real Vref30 speed so it is artificially bumbed up a bit for that reason. I'm no expert but it's what I've been told in the past.
cheers n beers.
cheers n beers.
