Go-Fly: one more minute than most?

[Stop Stop Stop]

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.

[timzsta]

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

[Mooney]

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!

[PaulDeGearup]

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.

[Sick]

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.

[Wee Weasley Welshman]

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

[Noctivaga]

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.:)

[Sick]

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.

[The Puzzler]

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.:)

[Stick Flying]

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.

[Safety's No Accident]

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 (http://www.pprune.org/forums/showthread.php?s=&threadid=51943&highlight=separation)

[Don Coyote]

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?

Don

[everybody]

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...

[Herod]

Just a point to those who are criticising: I can't see anywhere any statement that the aircraft was lined up.

[PaulDeGearup]

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?

[outofsynch]

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!

[Stop Stop Stop]

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.

[Crash and Burn]

Firstly, as everyone has pointed out, it is the captain’s 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!!

[Raw Data]

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.

[john_tullamarine]

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 ..

[Safety's No Accident]

I'm affraid to say it, but ATC also have their part to play in this - e.g. read my contrib on page one of this thread, and perhaps a fuller explanation of that might help:

A B757 is told to line up and wait, whilst an aircraft which just landed vacates.

The B757 is then issued take-off clearance and commences the role - and we're told to line-up & wait in turn behind the departing B757 - which we do.

We start our clocks (based on the start of the B757's role) and we're expecting ( neigh, assuming ) that ATC will be providing the normal two minutes between us and it.

The B757 lifts off pretty much as we apply the brakes to 'wait'.

It then comes as a surprise that at 50" we're issued with our take-off clearance - and at which some might be tempted to blast off down the runway.

We said that "we'd like the full 2 minutes" and to be fair ATC were fine about it - however we got the distinct impression that ATC were trying to 'hustle' us to be on our way (sorry guys, it's just how it seemed) probably because there were loads of other aircraft waiting behind us both to depart and to land.

Of course if ATC are expecting (hoping) that we'll accept an earlier than normal departure - i.e. reduced separation - in order that a landing aircraft can be slotted in behind us then we'd like to know about it PRIOR to lining up on the runway - so saving embarrasment all around, as we sit on the runway waiting for the proper separation, and ATC issue the "Go-Around" instruction to the fella who's hoping to land.

So I think the question I'd like answered is does the two minutes start from when the preceeding aircraft roles or from when it starts generating lift ? - there seems to be some confussion about this. Would any ATC folks choose to enlighten us as to what criteria they use for assessing when the timing for the separation starts on their clocks ?

Ps. A very valid point was made above by outofsynch - in that some here would seemingly be making no allowance for a wake turb encounter when you've just suffered a major mechanical failure of an engine, e.g. in my example above, we'd have looked a right couple of prats if at 50" we'd blasted off down the runway, passed V1, suffered an engine problem, got airbourne at Vr, and then flown into the wake turb of the preceeding aircraft - veritably "One hopes for the best, but expects the worst !"

[Wee Weasley Welshman]

On the specifics of this case we would need to hear the tapes.

"We need another minute" might imply a company policy. I might mean we as in the Royal we.

The Go book is clear - standard 2 mins unless intersections are involved.

Looking from a CRM stance:

Take off clearnance is given the Skipper is happy to go.

The FO pipes up "hang on - do we need three minutes behind him?"

-------

At this point the Skipper could say - "no - lets go".

OR

He could say "Tower we need another minute here - now Bob, the book says 3 mins from an intersection behind a heavy. So in this case we only need 2 is my view. Are you happy with that or if you want, lets taxi clear and double check, I don't mind".

-------

Which is the best CRM?

Perhaps thats what happened. We won't ever know.

Its always preferable to ask for extended departure prior to entering the runway. However a million and one reasons can distract you from doing so.

-------

We all know about the injustice of your split second decision being judged by a panel of experts with the benefit of hindsight and time on the subsequent board of enquiry.

We should be mindful of such injustice here.

------

Good and interesting debate though. A most excellent forum this i think.

WWW

[Pub User]

WWW

You're right, the discussion is over a ONE MINUTE difference. The CAA specifiy Minima, not absolute times, and it wasn't LHR at rush-hour.

Raw Data

The pax would, it's true, be concerned about a go-around, but they would be more concerned about a crash.

Airmanship is about informed judgements, not blind rule-following.

[doggonetired]

Firstly, excellent, thought provoking thread. It would appear that the original post was a question of SOP not airmanship and although as has already been mentioned we will never know the "conversation" that led to the response of "er um yes" to the question of Co. policy, maybe a slighty more "diplomatic" answer would have satisfied STOP STOP STOP's curiosity. However, I have a penny'th of thought for the debate and it's this,
We have this excellent tool called CRM at our disposal which we as pilots generally use to good effect, not least by trying to let everybody know what's going on in our "little world" so that they might plan the best course of action, so why do I feel that generally the offer is not reciprocated? Over generalisation it maybe and where I come from they are improving, by chipping away slowly ("track miles please, our number in the queue please, expected time in the hold if available please" etc.) but it always feels like the info is not given willingly. We can all play our part, ("unlikely to make the fisrt R.E.T., may we roll to the end? will 170kts to 5 miles be OK?")
On the vortex question our training Dept. agree with the earlier post that a practicle application of the recommendations is to time from the start of take off roll to your start of take off roll

I'll get my coat.....

[athene]

2 minutes: 120 secs wheels up to wheels up which is why the take off instruction is given maybe 30 secs early. Its usually longer than that though while waiting for preceeding to vacate, etc... hope that helps :)

[ATCbabe]

Just to back up what Athene says wake is from nose up till nose touchdown.
We do give take off clearance before the 2 or 3 minutes are up on the basis that generally take off roll takes about 30 seconds.
Any pilot can say he/she wishes an extra minute at any time and no ATC will force them off the runway. It's more than our job is worth, especially if that aircraft then experiences problems due to turbulence!
It would be nice if all pilots said they wish extra time before lining up especially when they can see something is bearing down on finals, but this isnt always the case. I know that from a personnal perspective I would rather send something around on finals than try and "force" any aircraft to take off when the captain isnt happy about doing so.
At the end of the day we all want to go home "fat and happy", not have to spend the rest of the day filling in forms and explaining why an aircraft was put in danger!

[crossfeedclosed]

Wake vortexes (?) really begin in earnest when the preceding aircraft rotates for taakeoff. Two minutes is the standard seperation from takeoff end and three if an intersection is involved. These are MINIMUMS. Take as long as you feel you need but do tell ATC before you line up. See CAA and FAA circulars on this subject, also see some videos readily available. It frightens the hell out of me ever since almost getting caught in a 737 wake (in a light a/c) years ago. Ignore it at your peril.

[grusome]

j_t,
I take it that you're alluding to the Boeing examination of the 737 loss-of-control some years ago. The video emphatically demonstrates the consequences of a hands-off, A/P engaged, slow crossing of the wake of a 727 at altitude. Four cameras are involved, one in the cockpit looking out at the smoke trail, one in a sort of panoramic mode on the top of the fin, and two looking at the instruments.
The fundamental problem is the back-stick applied by the A/P at about 90 deg of bank! From memory, Boeing's thesis is that unless appropriate action is taken, structural failure will occur.
Also from memory, this accident was the root cause of the introduction of real U/A training (sim) for QA and AN, an area not really addressed in heavy RPT prior to that video being circulated (despite, I might add, the multiple requests from Examiners over preceding years). Mind you, QA C&T knew it all!

Gru

[john_tullamarine]

Grusome,

There are several videos I have seen .. the particular one I was referring to (and, while I have copy it is, unfortunately, not at my side at present) showed a similar scenario with the 737 flying behind another aircraft with the 737 in the vortex field. The TP was hand flying as I recall and the interesting bit related to the magnitude of control deflections needed to keep the bird doing the right thing.

On the structural side, the levels of vertical gust which the penetrating aircraft can sustain are quite frightening. There was a very useful RAeS article some time ago which looked at the numbers for a 747 .. interesting.

You refer to the upset concerns and UA training. Both Boeing and Airbus produced similar, very effective, training videos on upset recovery which I think ought to be mandatory viewing for all.

I have some problems with sim training in this area ... the typical structured sim exercise which I have seen tends to be pretty tame and of limited value. If an ad hoc extreme upset is generated there is a concern regarding sim fidelity.

As a result I have tended to train through the structured scenario to justify the box ticking .. and then introduced the ad hoc upsets with appropriate briefing regarding fidelity. The standard recovery recommendations in the Boeing and Airbus videos can be applied in a resulting generic scenario. The result for pilot confidence is palpable ...

[snooky]

Stop Stop Stop refers to the wind at the time being 10kts, 60 degrees off, and therefore the vortices should not be a problem. I think that this is a common misconception.
As far as I know, the vortices tend to travel outwards at approx. 6 kts, so this type of wind would be ideal to hold them in the take off path.

[CrashDive]

I've fortunately not experienced (yet) a severe wake turb encounter on takeoff ( though maybe just a tadge of it ).

However, whilst once following a B747 into STN, I had my 737 roll from 25 right bank through to 45 left bank ( all accompanied by the automatic "Bank Angle" warnings ) - all in the space of about 3 seconds !

Similarly following a B737-800 into CPH one night ( indeed I latterly asked ATC if it was a B757 we were behind ) - whilst in a 25 right bank, to intercept the localiser, we were rolled to 40 left bank ( and again plus the "Bank Angle" warnings ) all in the matter of just a few seconds !

Nb. Both of these events occured when the spacing, according to ATC (and our TCAS), was deemed adequate ( read 'Minimum' ) !

And let's not forget that we had the luxury of several thousand feet of air between us and the ground - so let's all be carefull out there !!!

[Ignition Override]

Mr WW Welshman: that is an excellent description, which can also mean that there is no room in the cockpit for typical male egos in front of other guys or gals.

By the way, do male Captains try to be any less cautious with female FOs, or is the opposite situation more common?

Crash Dive: several years ago, a Lufthansa A-340 pilot (while waiting for hotel shuttle in San Fran.) told me that once while departing Munich, their very large Airbus suddenly rolled about 20-25 degrees because of a 757 just in front of them. If a 757 can cause an uncommanded roll in a A-340/330, then anything is possible.

[grusome]

j_t,
Sorry, been away.
I understand where you're coming from wrt to sim fidelity. However, I started to give some respect to the math model after an exercise in the AN 146 sim, when, during the B707 Coronial, we took the Coroner on a demo ride, trying to simulate the loss of directional control and consequences that had occurred at ESL.
After making allowances for some of the design features such as Vmca being below the stall speed, we actually got the sim to spin - or at least depart in a like manner to spin entry. Everything, including the visual, was presented in the expected way. As a matter of interest, it consistently took 6000 ft to recover, which met the criteria advanced by another expert witness.
Something to bear in mind when experimenting with big toys!
Also, despite the fears of the sim centre management, we didn't hit the stops or blow any hydraulics. All very interesting.
Cheers
Gru