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Go-Fly: one more minute than most?

Old 5th Jun 2002, 20:35
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Talking Go-Fly: one more minute than most?

Heard today at GLA a Go 737 (GO 344) tell ATC that they needed 3 minutes for a departure behind a heavy type (B767).

ATC queried if that was company policy. There was a long pause and the pilot said, "er yes."

The question is, is that really Go policy or was it either a Captain being over cautious or a mistake made on the radio but not owned up to.

It could have caused a go around if ATC were expecting a two minute wait like most others. Luckily it didn't.
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Old 5th Jun 2002, 20:48
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2 or 3 minutes, that is the question. However there maybe a greater point here.

Whilst the cause of the A300 crash in New York last year has yet to be officially published there has been speculation that the aircraft departed too soon after the previous aircraft. Avoidance of wake turbulence is important, particularly in critical phases of flight.

Secondly, it surely it is up to the PIC whether he takes off immediately following his clearance to do so, or waites for a further period if he has any doubts. It is he that is ultimately responsible for his aircraft and passengers, not the tower controller who would like to squeeze in the next landing aircraft as soon as possible.

Thirdly and most importantly - there was no accident here. No body was hurt or injured. So whilst the finer points of aviation law maybe in discussion, safety has prevailed - the GO pilot did not allow himself to get into a dangerous wake vortex situation, despite pressure from ATC. That's a well done in my humble book
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Old 5th Jun 2002, 21:06
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2 or 3 mins. It depends if the a/c departed from a intersection. I was at GLA last week and ATC cleared us for take off behind a AA767 inside the 2 mins. I dont know if ATC factor in any delay time between clearence to go and us actually moving.

ATC are very good in this country, GLA are usually good to us GO people!
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Old 5th Jun 2002, 21:39
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Stop x 3.

If you check the CAA website you will find AICs offering advice on departing behind heavy aircraft. Sensible chap that Capt. Just shows you cant simply buy experience.
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Old 5th Jun 2002, 22:07
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Asking for 3 mins at the hold would be cautious, asking for it after having lined up would be pretty dumb.

I always had thought it was 2/3 mins from start of roll to start of roll but I saw something official recently (I cant remember where) which said it was airborne to start of roll.
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Old 5th Jun 2002, 22:35
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Wink

2 mins is legal. 3 perhaps prudent in the prevailing conditions.

If you have been cleared to line up and then suddenly think " hang on - there's not much crosswind and I'm not too happy about this" then asking for 3 mins might well be a Very Good Idea.

Shame it didn't occur prior to entering the runway but sometimes that happens - checklists, cabin secure, FO wittering on etc. etc.

Better to cause a complete non-event (go around from 1000ft) than to enter a take off event with doubts. Surely?

It takes guts to get yourself into a situation which makes you unhappy-but-legal and then ask for something out of the ordinary to make yourself happier. If more Skippers and FO's had done this over the years then we might not have an annual CRM course...

I have no knowledge about this non incident whatsoever and only wish to comment in generalised terms as a junior FO.

I have found based on scant experience that the safest way of operating is to ask yourself - "Am I happy?". If there is the merest hesitation then you speak up and say "hang on - I need a minute here - are we OK with...".

Its often hard to do. 99 times out of a 100 you just expose your inexperience and/or ignorance of something that you should be aware of. But THAT IS the professional thing to do. THAT is CRM in day to day practice. IMHO.

Every attempt to make ATC's life as easy and predictable as possible is made in every Brit airline I imagine. But sometimes odd things happen and you ask for something unexpected. The hesitation to do so is probably more hazardous than the reuslt of doing so.

Maybe.

I am mindful of speaking from very limited experience. But it is my honest opinon.

Cheers

WWW
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Old 5th Jun 2002, 23:34
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Thumbs up

WWW-- Your scant experience, and limited background appear to be sufficient to provide you with an excellent awareness. It would be so lovely if those with vast experience could be equally well informed.

Good on you for your attitude. This is indeed a non-event because for whatever reason the Captain chose prudence. He saw a potential problem, or whatever, he communicated with the controllers, he provided a plan of action, he executed the plan safely. Sounds like the kind of guy we should all aspire to be, as opposed to pedantic rule citers.
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Old 5th Jun 2002, 23:49
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given that the ICAO minimums are calculated on worst case scenarios (ie a light crosswind), I am at a loss to think of a need for increasing the spacing.

I vaguely recall someone telling me about GO having done this once before causing one or more go arounds at STN too.
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Old 6th Jun 2002, 07:00
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Question

Puzzle me this....

When does a preceding aircraft produce wake? Once it produces lift. I always start the timing from rotation, not start of take off roll, for this reason. That gives me another 30 second delay....who is ever in that much of a hurry. This GO captain acted as he should have.
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Old 6th Jun 2002, 08:04
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I dont believe anybody has answered the question.

As one who could be warned of a late landing clearance I would sorta like to know in advance that the GO lined up in front is going to need more time due to company restrictions. I personally believe all go-arounds have an element of hazard (particularly for those operating out of Paris CDG).

I'm always one for safety but lets be careful not to throw the ball into other's courts. If it is company procedure we all should be aware of it.
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Old 6th Jun 2002, 08:11
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Likewise for us too - out of a major London airport - on Tuesday.

(In a B737) We're told to line up and wait behind a departing B757 - an aircraft type that's renowned for particularly vicious wake turbulence - and very shortly after said aircraft rotates, we're also cleared to take-off.

Nb. The wind on the day was light.

Us - "Err, we'd like at least two minutes between us and the 757"

Tower - "No problem"

So we waited - and it admitedly seems like forever, and "yes" you feel like a chump for holding up the departures - but as is said, 'It is always better to be one minute late in this life, than years early in the next !'

Ps. Please also have a read of this excellent / explanatory thread Takeoff delay behind a 757
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Old 6th Jun 2002, 08:48
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As has already been aluded to, if the heavy used the full length and the medium uses an intersection then 3 minutes separation is required. Does anybody know if this was the case here?

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Old 6th Jun 2002, 09:21
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Don't have the paperwork to hand, but I'm pretty sure the rules say the timing should be from airborne to airborne. So either you know exactly how long your take-off roll is or you're practical and assume it's about the same as the preceding, give or take a few seconds, and time from start of roll. You can only get so scientific.

What's really important is to know when it matters. I was surprised to discover that it's not in calm conditions. In this case the two main vortices spread out to either side of the flight path and settle slowly. Assuming both aircraft track straight, you go up the centre and rarely encounter one of them.

It's worst if you get a light wind with a small component across the runway. Then the vortices don't dissipate but drift slowly sideways as they settle downwards. So you'll be into the upwind one pretty soon into the flight so delay or expect it !

It gets even better. There's a minimum distance below which an intersection is not considered as such. I don't have it to hand, but it means some of our intersections actually count as full length.

It's a lot more involved than some people are making out. So how can you criticise an experienced professional doing his job well ? He was taking into account all these factors and probably many others so please let him get on with doing his job safely...
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Old 6th Jun 2002, 09:29
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Just a point to those who are criticising: I can't see anywhere any statement that the aircraft was lined up.
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Old 6th Jun 2002, 10:29
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Just a point to be picky but this an interesting discussion so please dont regard it as any form of criticism.

Surely the turbulence on departure takes 2 forms - engine wake i.e jet thrust turbulence (sit behind a heavy 744 and see what i mean) and aerodynamic wake turbulence.

As the wing will generate lift as soon as the air starts to flow over it some wake will be generated.The rotation point is when the L/D and Wt/Thrust couples are sufficient to get the aircraft airborne but as the airplane accelerates on the ground lift and thus wake will be generated throughout the take off run.

This may not have such a great effect on a largish jet e.g 737 but on a small turboprop e.g J31/41/ATR it may be significant.

Anyone have a source of definitive info on this subject, other than the AICs?
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Old 6th Jun 2002, 11:55
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To answer the original question... Go Ops manual exactly as AIC etc recoommendations. 2mins same t/o position or 3mins reduced length. These are MINIMUMS! Especially as in engine failure etc you are likely to climb below the preceding flightpath, and possibly drift aside a little.

Very prudent decision by Captain, as as many have said before here. Too late thinking about it as you pass 90deg aob!
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Old 6th Jun 2002, 19:24
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Just to put the event in question into context and to answer some queries about the day in question:

Both departures were full length, ie. from the beginning of the runway...no intersection problems here.

There was a 10 kt wind sixty degrees off the runway. No vortex staying on the runway considerations here.

My basic point, and that which has not been answered is that of whether it is GO POLICY to allow 3 minutes behind a heavy from the same point on the runway. If it isn't then all you Go flyers may well find you get it anyway now at GLA because that is what your colleague told ATC. Is it policy, or was he telling a porkie?

Of course it is down to the commander to extend that time between departures...that is always his privilege, but in this case, would it not be prudent to say "I would like 3 minutes behind the departing" prior to entering the runway, particularly as you have sat in the queue behind him for the last five minutes.

I would not be too impressed if I had to do a low level go around if there was an aircraft on the runway making an (in my opinion) unnecessarily long wait behind a heavy in good conditions, when ATC had not been informed to the contrary. ATC will always expect you to conform unless you tell them otherwise. Lined up on the runway is not the time. Try something similar at Manchester and you will be told to vacate. How many have incurred the wrath of ATC at Edinburgh when you backtrack without telling the ground controller that you need to.

A simple answer to my question would be nice.
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Old 6th Jun 2002, 21:29
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Don't forget to tell A.T.C.

Firstly, as everyone has pointed out, it is the captainís decision when he/she decides to roll. There is no holding bays at EDI, and the captain must have seen the one ahead all the way along the taxi route. Perhaps he could have mentioned his "requirement" eariler (i.e. before entering the rwy) rather than as ATC cleared him/her for T/O.

Secondly, there is no requirement for three minutes for a full-length departure after another full-length departure of a higher vortex group. The SOP is two minutes; every airline uses the same rule. If the C.A.A. where to give out exceptions to various airlines flying the same aircraft type, then it's hardly SOP. It would be impossible for ATC to remember which airline is doing what with each aircraft type.

Thirdly, what do you think the delays would be like at LHR, LGW and other busy aerodromes if everyone added a minute or two when they felt like it? LHR shifts on average 42 per hour, that's one departure every 1 min 26 secs (slightly less in fact, good show chaps!!). They have been doing that for years! In contrast in the U.S., the commander can "wave" departure vortex requirements in order to expedite his/her departure. Foolish to do so some may say; then again it could be argued if there were a strong cross wind, the vortex wake would be blown away. From what I've read the cross wind neads to be quite strong indeed.... Note I'm not going to mention a figure!!
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Old 6th Jun 2002, 22:50
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Engine "turbulence" dissipates very quickly and is not a threat (unless you are in a light aircraft). it is just fast-moving air, which your aircraft will shortly be flying through anyway.

The danger comes from wing-tip vortices, and their ability to upset the aircraft. These are most pronounced at high angles of attack and when lift produced is greatest (to put it crudely). Rotation is just such a time, athough vortices are produced from the moment the aircraft starts to move.

WWW says a go-around from 1000 feet is non-event. I beg to differ. It is a simple manoeuver, however it can be very, very upsetting for the pax in the back who may well take their custom elsewhere if they have a bad experience. Seeing as how they pay the bills, it may be a good idea to upset them as little as possible- unnecessary go-arounds don't help.
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Old 7th Jun 2002, 03:48
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Could I suggest that you check with your training people for a good little video Boeing put out some years ago.

The video looked at the sort of manoeuvring required by a 737, as I recall, flying in trail and in the vortex circulation, behind some bigger units ...... at varying distances which were typical of wake turbulence separation standards.

Makes for interesting and sobering reflection.....

If your company hasn't got it .. then agitate for the relevant manager to get it ....... too valuable a message to miss ..
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