777 Gear drop

[Fishaman]

EK39 B777 A6-END passed overhead this afternoon on finals to BHX, my question is when is the normal time during approach to drop the gear, she was approx 8 miles out at about 1700ft (I used FR for latter) and yes she did make the tarmac!

[HEATHROW DIRECTOR]

Would normally be a little higher at that range, but never trust FR24! I bet the crew knew what they were doing.

PS It's "final" not plural.

[Green Guard]

Aircraft must be STABILIZED i.e. with Landing Flaps and LG down and locked and checked
not later then 1000 feet AFE on IMC App
not later then 500 feet AFE on VMC App
....
So 8 NM is far enough even for IMC App

[wiggy]

Without knowing the full circumstances it's impossible to say one way or another.

If flying a level "platform" for a close in intercept of the glidepath/visual approach then 1700 agl for the gear selection isn't out of the question...

then again if you're descending on the more traditional ILS 3 degree slope then 1700 feet above the airfield is probably about as late as most of us would want to leave it...

then again as HD has implied ... if you're 8 miles out from the airport and on a 3 degree slope you should be about 2400 feet above airfield level, and FR has it's limitations....

[DaveReidUK]

if you're 8 miles out from the airport and on a 3 degree slope you should be about 2400 feet above airfield level, and FR has it's limitations....

Later on during the same approach, UAE39 descends instantaneously from 1300' to 400'. That should tell the OP all he needs to know about the reliability of FlightRadar24 height readouts.

[kcockayne]

Fishaman

I often watch aircraft on final from home (6mile final) visually; &, although they are usually no larger than A320 size, they drop the landing gear anywhere between 8 & 5 miles from touchdown.

[Fishaman]

Cheers guys, I usually see both EK flights (soon to be thrice daily) on final into BHX and she did seem to be very low today in regards to that location.
I get the message re:FR

[Curious Pax]

Out of curiosity - do speed requests from ATC make a difference? I can imagine (quite likely wrongly!) that a higher speed approach, say to 10 miles, would then need a more pronounced reduction in speed, which could require an earlier gear drop as that would create more drag. A slower approach could mean a later lowering as it would then require more thrust to maintain speed due to the increased drag (= noise on the ground), which it would be preferable to keep to a minimum (safety permitting of course).

Or does that play no part in the decision process?

[wiggy]

a higher speed approach, say to 10 miles, would then need a more pronounced reduction in speed, which could require an earlier gear drop as that would create more drag.

In extremis yes, though it's speedbrake first to get the drag, gear's a bit of an untidy option but there if you really need to decelerate.

. A slower approach could mean a later lowering as it would then require more thrust to maintain speed due to the increased drag (= noise on the ground), which it would be preferable to keep to a minimum (safety permitting of course).

True, but it's pretty much industry standard that regardless of ATC's wishes the aircraft must be fully configured (gear locked down, landing flap achieved) at 1000 feet above airfield level. To achieve that whilst descending on a 3 degree glide requires gear lowering to start well before 1000'.

[El Bunto]

Later on during the same approach, UAE39 descends instantaneously from 1300' to 400'. That should tell the OP all he needs to know about the reliability of FlightRadar24 height readouts.

Probably best to understand how systems work before you bash them.

If you're watching FR24 in replay mode you will see sudden height and course changes because FR24 dithers the data for storage, to reduce storage requirements. Data interval is in the order of 24 seconds. That's the same reasons that turns on replay tracks looks jagged and angular.

However if you're watching in near-real-time the 'height readouts' and course changes are just as smooth and reliable as Mode-S permits as all received data is being used at that point. Default display refresh interval is eight seconds.

[wiggy]

Probably best to understand how systems work before you bash them.

Thanks for the info - I'm not sure any "bashing" was involved, from what you've said it seems like a fair observation, i.e. don't rely on FR24 for detailed forensic analysis of historic flight paths.

[DaveReidUK]

Originally Posted by El Bunto

If you're watching FR24 in replay mode you will see sudden height and course changes because FR24 dithers the data for storage, to reduce storage requirements. Data interval is in the order of 24 seconds. That's the same reasons that turns on replay tracks looks jagged and angular.

Thanks for the confirmation that the approach profile the OP observed is unlikely to be what actually happened.

Originally Posted by wiggy

i.e. don't rely on FR24 for detailed forensic analysis of historic flight paths.

Succinctly put.

[Dockwell]

https://www.youtube.com/watch?v=KDgvWa-EbbE

[777fly]

The B777 low drag/ low noise approach is flap 5 gear up. In still air this can be maintained to 2000ft (about 7 miles) on a 3 degree approach. At this point the landing gear is lowered and flap 20 selected. Airspeed reduces and at about 1500ft (5 miles) landing flap can be selected. The speed then reduces to Vref+5 just before 1000ft, which is the first 'approach gate' for a stabilised approach. A tailwind or headwind would move the gear selection point up or down the approach +/- a mile.

[Monarch Man]

The B777 low drag/ low noise approach is flap 5 gear up. In still air this can be maintained to 2000ft (about 7 miles) on a 3 degree approach. At this point the landing gear is lowered and flap 20 selected. Airspeed reduces and at about 1500ft (5 miles) landing flap can be selected. The speed then reduces to Vref+5 just before 1000ft, which is the first 'approach gate' for a stabilised approach. A tailwind or headwind would move the gear selection point up or down the approach +/- a mile.

The EK stabilisation criteria is a little more conservative, the first gate is 1500 AAL, and the low drag profile at high LW in a 300ER is F15, at F5 the drag doesn't overcome the intertia of landing at 240-250T, which invariably happens into Brum.
Gear down F20 at 2000AAL, and landing flap selected by 1500.