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General Discussions => General Discussion => Topic started by: bradley27 on May 19, 2013, 12:20:13 PM

Title: 777-300ER Gear down over London (Real world)
Post by: bradley27 on May 19, 2013, 12:20:13 PM
I was at Vauxhall rail station (same place as the Helicopter crash some months ago) yesterday evening and all the inbound Heathrow flights were passing right over me...a 777-300ER Cathay Pacific then approached and had its gear down already before it had passed over the station, was quite strange...it was very low. I have been at Twickenham station before early in the mornings and you can see these flights on final approach to both 27R & 27L dropping their gear just past the Richmond area so i was quite interested to know why the gear would be down so early...on the same note i didnt know Heathrow opened both runways to arrivals in the early mornings...was very interesting to see all the heavy long hauls rolling in...Royal Brunei, BA, Virgin, South African, Gulf
Title: Re: 777-300ER Gear down over London (Real world)
Post by: Er!k on May 19, 2013, 12:25:35 PM
Interesting! Maybe they lowered the gear early to reduce the speed?
Title: Re: 777-300ER Gear down over London (Real world)
Post by: bradley27 on May 19, 2013, 12:30:49 PM
Maybe, it didnt look any faster than the 767-300 before it but then again that is just an observation from the human eye..

The small circle is vauxhall station where the gear was already down...the bigger one is where you would normally see the gear being lowered
Title: Re: 777-300ER Gear down over London (Real world)
Post by: benclark on May 19, 2013, 01:18:38 PM
Speed control, possibly but unlikely I would imagine, that's why they have spoilers. More likely would be a possible "emergency" involving the hydraulic system, remarkably common so quite possible they lowered the gear early to make sure they even could.
Title: Re: 777-300ER Gear down over London (Real world)
Post by: atco on May 19, 2013, 03:49:23 PM
Maybe, it didnt look any faster than the 767-300 before it but then again that is just an observation from the human eye..

The small circle is vauxhall station where the gear was already down...the bigger one is where you would normally see the gear being lowered

I think its fairly standard to be honest Bradley - maybe  a touch earlier than usual but not enough to be out of the realm of normal ops.
Standard speeds into LHR is 180kts on base and 160 on final to 4dme. This almost always requires gear down on glideslope intercept - Tough to hold 160 in descent without a serious amount of drag, especially in a 777. So if the glide is intercepted at 4000 that would be around 12-13 miles out.
I have never seen the gear being lowered over Hounslow, thats way too close, only around 4 miles or so - about the time the aircraft has to be slowing to final approach speed, which would be done with flap. Relatively standard ops would be 180 on base at flap 1 or 5 (Boeing degrees used here), then turn final and slow to 160 at flap 10. On G/S intercept gear down and flaps 20 then at 4 miles to slow to Vapp flaps to 25/30/40.
Pretty much every airline has SOP's for stabilised approach criteria and usually that means speed in a set range, minor or no deviation from loc and glide, specified descent rate and gear and flaps down.

It may be a little on the early side, but again it depends on where glidslope intercept occurs - from 3,000ft that would be at 9-10 miles out, but at 4,000 that would be 12-13 or even at 5,000 that would be 15-16 miles out. It would be pretty hard for a slick aircraft like a 777 to hold 160kts and descend on the glideslope without dropping the gear.

Edit - Also Ben most airlines ban use of spoilers with the flaps below a certain level because that breaks stabilised approach criteria. If you are needing to use spoilers on final approach you are not stable and therefore have to go around. Obviously varies by company but the big airlines prohibit spoiler use during the final segment.
Title: Re: 777-300ER Gear down over London (Real world)
Post by: Kyle M. on May 19, 2013, 04:02:15 PM
I remember going to Heathrow and seeing the gear lowered seemingly even with Windsor Castle (East flow). Was a little surprised with it as it seemed like it a lot later than what I'm used to in the States. Noticed the same at other European Airports as well.

Kyle
Title: Re: 777-300ER Gear down over London (Real world)
Post by: M-Sauce on May 19, 2013, 04:28:39 PM
Some of the LHR flights, especially the morning ones, are slot restricted. This means not landing before the slot time, and ATC is damn good at spacing you in order to achieve that to within seconds.

Keep in mind you can't use landing flaps unless the gear is down. Well, you can, but then you will have the config / EGPWS blaring at you. So in order to slow to final approach speed, you need to drop the gear and then you will be able to select the landing flap setting which will give you the lowest approach speed. In the 400, anything past Flaps 20 without the wheels down will give you warnings - and then you gotta file paperwork, which really sucks after a long haul flight (Big brother.. er, I mean FDAP - is always watching!).

So wheels down early was probably to achieve approach speed due to slot or traffic.

 ::cheers::
Title: Re: 777-300ER Gear down over London (Real world)
Post by: vc-10 on May 19, 2013, 07:29:06 PM
Gear was quite often being dropped around Windsor/Dorney area when landing on Runway 09L/R, at least when I was living up there. Always gear down by Windsor, anyway.
Title: Re: 777-300ER Gear down over London (Real world)
Post by: benclark on May 20, 2013, 02:51:46 AM
That's interesting about the spoilers, I know I've seen them deployed on smaller birds A32X/B737 for example when I've been onboard during final approach although it is only 1 or maybe 2 degrees, very minor deployment (and yes not part of the aileron's as both wings were deployed) but yeah now that I think about it not sure I've ever seem them deployed on the approach on the bigger birds that I've been on.
Title: Re: 777-300ER Gear down over London (Real world)
Post by: M-Sauce on May 21, 2013, 01:54:27 AM
That's interesting about the spoilers, I know I've seen them deployed on smaller birds A32X/B737 for example when I've been onboard during final approach although it is only 1 or maybe 2 degrees, very minor deployment (and yes not part of the aileron's as both wings were deployed) but yeah now that I think about it not sure I've ever seem them deployed on the approach on the bigger birds that I've been on.

Most airliners have roll spoiler mixing, but you are right, they should not stay deployed for long when being used for roll. On the -400, we have a limitation of not having speedbrakes deployed with flaps more than 10 in some frames, and others it is flaps 20. Most crews just make sure they don't deploy them with more than flaps 10 to play it safe and cover themselves. Then again, if you have speedbrake out with more than flaps 10, something has gone pear-shaped and you should probably stow the brakes and come up with a different plan. Not to mention the speedbrakes are pretty much worthless below 200kts, they have very little effect.

 ::cheers::