Weather avoidance and ATC
 

Earlier today i was flying into a busy airport where there was alot of weather in the TMA. Also it was very busy at the time.

Now some aircraft were telling ATC, i'm heading xxx to avoid. Other aircraft were requesting xxx due weather and waiting for clearance. At the same time some departing aircraft were constantly requesting further climb/descent as they were levelling off (no weather avoidance so as far as i'm concerned these guys/gals went to the back of the que). However alot of aircraft and ATC were stepping all over each other and there were many many garbled transmisions. Was a bit of a mess and the service provided by the guy on approach was absolutely fantastic. I can imagine he's since gone home and collapsed on his bed in an exhausted heap.

However my question is when cb's and other aircraft are a factor, what do you do. Request and wait for approval or just tell atc what you're doing. (remember TMA not enroute)

For those wondering what we did. We told ATC we're doing xxx because the red on the radar screen was getting very close and there was very little space to manouver. clouds to the left of me clouds to the right of me stuck in the middle for all you steelers wheel fans.

Having been to a NATS TRUCE day the answer in the UK is most definitely wait for a clearance.

One of their closest "Near Misses" of last year was caused by just the situation you are describing. A very busy London TMA, lots of wx avoidance and lots of stepping on each other. A Biz Jet decided to avoid without getting a clearance and they caused a serious loss of separation with an Air Lingus on departure from Heathrow. (And of course someone saying TCAS RA is yet more talking and confusion on the frequency)!

The word from NATS is that if you can't get a word in, and you MUST turn to avoid WX, you should squawk 7700. This will cause you to show red on their screens. They will stop all other communication and ask you what the problem is. You can then tell them you are turning due to weather.

Your target going red will also immediately draw their attention to you and enable them to move aircraft out of your way. Controllers operating the sectors above or below the sector that you are in will automatically stop any aircraft climbing or descending through your level when they see a 7700.

I admit it does seem strange squawking 7700 when you are not on a Mayday, but this is what NATS want us to do.

I'd also highly recommend going to a TRUCE day. It's a real eye opener and very interesting.

SW

Okay so what happens when several aircraft start squaking 7700. There were alot of a/c needing avoidance at the same time.

Agree on the TRUCE, went on one a few years back at the new prestwck centre before it opened. Very informative for both us and the new contollers. Unfortunately weather never came up. No of the aircrew or ATC bods thought to think of it. (big D'oh moment on my front)

Hi,

Is it not possible for ATC to anticipate weather problems by allowing CBs to be painted on their screens? In anticipation of the extra work load, an additional frequency and controller could be allocated.

hey,

where you flying into indra gandhi international airport - delhi? ( vidp)

your description sounds so much like that place. ATC has no idea whats going on and the pilots are doing their own diversions. just one big recipe for disaster.

No not india. If you read my initial post I state that the controller did an excellent job in trying to sort out the mess that all these cb's were creating. As to the weather on controllers radar screens, I'm lead to believe these are filtered out. ?

Cortilla is correct.

UK radar screens filter out the weather.

Whereas 30 mins. flying time East in the Amsterdam FIR the controllers can see the weather and just vector traffic around it without being asked. Guess which is the best system. :ugh:

You do NOT squawk 7700 if you are turning to avoid wx and require ATC attention. That is the most ridiculous piece of advice I have read on this forum.

:ugh::ugh::ugh:

Aviophage
 

Have you ever been to a TRUCE day, do you read what other people post. But then you probably don't need to given your superior knowledge.:rolleyes: Under 50 posts and it a shame it's not 5000 cos the whole of the aviation world would've been changed by now. That is if anyone had agreed with you.

I've read quite a bit on various threads here but not so many bits of dogmatic :mad:' in so few posts. Nonsense here about the squawk with no source to back it up (nonsense somewhere else too about anti col/strobe lights).

We all have so much to learn. You especially it would seem.

S

I have been vectored around weather in Ireland and in the USA, with an amazing precision. Dunno about the UK, but with todays toys for controllers, most places you can get an overlay of the weather on the radar screen. It makes of course the airplanes more difficult to see...

In Africa, I had the opposite, where only primary radar would get us lost in bad wx, and ATC comes up and says...:"ah, no more vectors, can't see you, so self position for the approach..." :}

Most of times, I just ask ATC, but when the time comes and you can't step in to talk, I just avoid and notify later. Rather have a well flown TCAS RA, than an aircraft pitted with hail stones... :ouch:

Flex

lol, thanks for your input.

You obviously think it's ok to deviate from an ATC clearance without telling anyone then?

You'd best have a chat with the people at the NATS training centre if you think that they are giving out ridiculous advice.

They went to great lengths to try and persuade us pilots not to be afraid of using 7700.

They also went to great lengths to persuade their controllers to get aircraft to squawk 7700 if unable to comply with a clearance for any reason.

In another case explored at the TRUCE session an Easyjet aircraft was unwilling to climb and take certain vectors after receiving a huge lightning strike. The aircraft was not on a PAN or a MAYDAY, but they'd just received a massive strike, lost a couple of minor systems and wanted to divert back to LGW without going near to any other weather. The controller was very obliging, but in doing so became extremely overloaded since other aircraft kept entering his sector and this EZY was in the way. The trainer impressed upon the controllers that amongst other things the EZY should have been made to wear 7700. This one action would have stopped other aircraft entering his sector and allowed him to deal with the difficult aircraft.

Not my rules and I'm not making this up for the fun of it.

If you don't like it, don't do it. (that assumes you're a pilot)

But before spouting off on here I suggest you speak to the NATS training department to get their opinion.

SW

I do agree with that statement, however

TCAS is the last line of defence and we should never let it get to that stage.

Secondly an RA can cause further loss of separation against other aircraft in a busy TMA

squawking 7700 would add another line of defence and hopefully prevent it getting to a TCAS RA.

Really wondering why all radar controllers don't have some sort of weather representation these days... The technology must exist as some have it, and it makes life much easier for everyone involved.

Back to the original question, I will request heading xxx when I have the time and/or I would like to avoid, and this only if the situation allows. I will state that I require heading xxx when continuing is completely unacceptable, but never turn before I get a reply.

S.

I agree. 7700 is saying "I am in deep sh!t!" (and usualy
acompanyed by a mayday call). Your not in deep sh!t by
avoiding weather cleared or uncleared. Sqawking ident is
the best way to draw ATC to your blip if theres too much
bloodey racket on the radio.

Just as 121.5 has degraded to a chatter freq (esp in SE
Asia) 7700 will be degraded to nusance value if the wolf
is cryed too often.

Cortilla, what does your AIP say to do? ours (Australia) says, request clearance, if a clearance can't be given broadcast a PAN PAN and do what you have to do to stay safe.

I don't fly through Cb's. They are dangerous. If the frequency is too congested to request avoidance, and deviating from my clearance could result in a loss of separation, then on the contrary I am in deep sh!t.

I agree Spin. So what will you do when your confronted with
a thick line of nastey 45,000 footers and have no choice but
to plow through em? Your infering you have no experience. :bored:

BTW "deep sh!t" refers to the posibility of losing your life.
If you cause a reduction of separation your not in deep
sh!t. A loss of separation is a different storey and between
you and the authority who issues your licence. Personaly I
batten down the hatches and plow through the muck till I
can get safely clear than risk plowing into another aircraft.

You always have a choice, at least you should have. If you literally have no choice but to fly through a line of 45000 footers then you have well and truly blown it somewhere back along the route. What circumstances do you have in mind that would tempt you in?.

sometimes there is another option ...
 

plan a route that avoids the area of severe weather, (severe TS walls over the Alps is a reasonably frequent example).
not always possible, but when it is, take the safest option and explain your extra fuel requirement and routing to ops, if not be prepared to sit it out until more information is available: don't get airborne and "hope" for the best.

Have seen lemming like behaviour on STAR's resulting in several lightning strikes to several planes within a few minutes , end result : several AOG pending engineering attention, when all they had to do was to request a routing to another STAR entry point.

If it is there, and you know it is there, try and deal with the problem at the planning/ briefing stage.

I think a point needs to be made about the original question in the thread;

Weather avoidance "in THE TMA." Not at altitude. That is a different set of circumstances and I think the regs already cover most contingencies in thas regard.

At altitude our TAS is very high, therefore it behoves all of us to ensure timely weather avoidance. Transport aeroplanes will come apart inside these Cb walls at 8 miles a minute! So do whatever you have to do, get off track, climb, descend away from traffic, broadcast intentions, etc, etc. (All things that have been rightly noted in this thread.)

However, in the TMA, I think a little more mental latitude is called for. Our speed is lower, our airspace is extremely limited, and we are in close proximity to both other aircraft, all trying to avoid, and of course, terrain.

ATC have a job to do, so try and make it easier for them... give them options."I require heading xx for xxmiles to avoid" That helps him plan. If he can't help you he may give you an alternative (then again, he may not, so be ready for it) If all fails, you may have to be prepared to ride it out, or hold clear. With only minor exceptions, worldwide, I've yet to see weather below the freezing level that will bend a transport aeroplane. Sure it'll shake you up a bit, so batten down the crew early if you know you're going to be in the thick of it and be prepared to ride it out at minimum penetration speed.
If it is really that bad, and you dn't want to push on, then hold clear of the weather (at least ATC can plan around you as a fixed point in space then) The Final approach requires more caution of course, as you are configured with a lower g-tolerance and windshear is your biggest threat, so by all means AVOID./ Hold/whatever.

But for goodness sake, don't make a bad situation worse by self vectoring in proximity to other traffic...who may be 'self vectoring' unannounced themselves! ATC will hardly be able to rescue you then: Imagine a multiple TCAS RA event going on WITH weather avoidance by other traffic! As to the A7700 option.... I'm not convinced that'd be a good idea. Certainly NOT in most 2nd and 3rd world ATC environs.( I stand to be corrected, happily if it becomes ICAO promulgated practice, of course) It'd cause total confusion and almost certainly would not get you the result you need. Remember this is a TMA situation here... you simply don't have the space.

The certification regulations don't quite agree with you here. It is not your TAS which counts here, it's the dynamic pressure. At high altitude, at cruise airspeeds, the dynamic pressure is not as high as at medium altitudes. The gust limits which the aircraft structure must adequately resist (plus a safety factor) actually decrease for higher flight levels. Here is the current CS 25.341 (a) 5:

PBL

Considering the lack of space for us pilots and ATCOs, my practice has been to avoid the problem by having and briefing a clear route free of weather in or out of the terminal area. I have have bad memories of holding much too close to weather on the arrivals to KATL, too many times. One particularly bad afternoon at SINCA where the pax had all their window shades down after we landed. The TMA is just too compact.

I do agree with A7700, it's better than keeping your maneuver a a secret. BTW, I fly a Global, so I have more flex than you airline types

GF

PBL
 

I think you're missing my point somewhat! The main thrust of my post was to do with the philosophy of assessing the criticality of weather avoidance at all costs, as opposed to looking for the path of least resistance, and mitigating further threats to the operation.

The other point I was making with regards to TAS was purely one of increased momentum at altitude. For a given gust vector, an increase in TAS (for a given IAS/EAS)will result in a greater resultant displacement vector from the flight path. And we all (hopefully)know what that can result in...

Cheers

If you are trying to make a point using mistaken ideas about aerodynamics, then you are failing to make your point. If your point is well taken, you should be able to make it without using mistaken reasoning. So best to try, no?

As far as I can interpret it, this statement seems to be misleading as well.
You talk about a "resultant displacement vector". "Resultant" is a technical term in dynamics for what you get by summing two other vectors, in this case they must be distance vectors. But I don't see those in your story so far. There is a velocity vector in the direction of flight path, and an acceleration vector, caused by the gust, normal to it. To get a resultant, you need to sum distance vectors, or velocity vectors, or acceleration vectors, but you have so far only adduced one of each, so there is no "resultant". Maybe you mean "resulting"?

Here is an argument to the exact contrary of your conclusion.

A displacement from the flight path is a function of acceleration normal to the flight path, and duration of the force causing the acceleration (the lift engendered by the gust). The lift engendered by the gust will be dependent upon the coefficient of lift, which itself is functional on the angle of attack. And those goings on are described by EAS, with two exceptions. One exception is the duration of the force, which, for a fixed gust domain, is less when TAS is higher. The other exception is the AoA in the gust, which is the angle of the resultant vector of the velocity of the airplane and the gust velocity normal to the airplane velocity. (Let us ignore the difference between geometric angle of attack and effective angle of attack for the purposes of this discussion.)

For purposes of aerodynamics, gust velocities are taken to be EAS (see CS 25 for examples). Let us fix the EAS of the airplane and the gust. The resultant velocity vector will have a specific angle to the velocity vector of the airplane, and this is AoA. This will generate a specific lift, which will accelerate the airplane upwards, and of course this acceleration will change the airplane velocity vector, so the AoA will be continually changing during the encounter. The divergence from flight path is a function of this, which one can obtain by double-integrating the acceleration, which is functional upon the continually-changing AoA. The salient point here is that, for a given EAS of airplane and gust, and given initial AoA of the airplane, the displacement from initial FP is a function of the duration of the gust.

Now, for a given lateral gust size, if your TAS is higher, you will be through the gust faster, that is, less duration of exposure. That means, according to the reasoning above, your displacement will be less than if your TAS is lower.

This is the exact opposite of the situation you want us apparently to assent to: you claim the displacement is greater.

So which is right? Is the displacement greater, or less, for a higher TAS but all EAS's the same?

To summarise, I am not yet convinced that .

BTW, if your "main point" is that weather avoidance is a good thing, I agree, for the paying passengers as well as the pilot. But weather avoidance is a more complicated issue than just not going where the red shows. Consider ice-particle icing, for example. That can ruin your day also.

PBL

Hmmm...

How to take a simple question about weather in and around the TMA and turn it into something extremely dull..

Thanks.

This debate has been round before.

The pilot in command has final responsibity for the safety of the flight. No one else. It is the pilot in command alone who decides what is safe and what is not and if they make an informed decision that avoiding a CB before being able to get clearance is the safe option then the law backs up that decision 100%.

Yes if one can ask or advise ATC about what is happening then that is the preferred option.

However, I am worried that ATC are saying no-no-no to the idea of (when necessary) avoid first and tell later simply to avoid having 2.5nm between two blips when there should be 3 and this pressure to do something unsafe could lead the less experienced into a lot of trouble.

Thinking of the LTMA situation, there is far too much pressure on people to maintain departure rates when lots of CB's about and that is what causes most of the fear.

If there was traffic avoiding weather all over the place and the avoiding traffic could not get a word in and they subsequently had to rely on TCAS to avoid a collision (not simply a loss of separation) then the biggest question would be why the departure was permitted?

The question always comes round about weatehr being displayed on ATC displays. Every time it is asked of NATS the answer "we have the weather filtered out" comes back..........which was a great answer in the 1970's when it was good not to have aircraft disappearing into the weather.

However, they seem to have not realised that today it is possible to have a colour real time feed from the local weather radar as a selectable overlay on the display when required. The information is fed as far as the ops room but that is all. and the reason why they won't do it - money.

So when I can't get a word in edgeways and use my display of the dangerous area of weather ahead to avoid it in the interests of safety don't complain because if money was not put before safety you could have the same (if not better) information when you need it.

As for the 7700 squawk all I can say is this suits the statisticians perfectly and the printouts will not have an airprox due to weather avoidance wearing two standard (orcam) squwaks.

Next we will have -

ABC123 turning right to avoid.

ATC - Negative continue heading 360 maintain 2000ft

ABC123 is now heading 090 at 3000ft

ATC - You turned and climbed without clearance. I am going to send a report and your stupid captain ass is toast.

ABC123 - can you please include in your report the fact that we avoided opposite direction traffic at our level. :D :D

At last, some sense.

DFC is spot on, remember the ATCO does not have his backside strapped to that aircraft, we do.

<<However, they seem to have not realised that today it is possible to have a colour real time feed from the local weather radar as a selectable overlay on the display when required. The information is fed as far as the ops room but that is all. and the reason why they won't do it - money.>>

It's 8 years since I retired from LATCC. At that time there was a weather radar display in the ops room connected direct to the Met Office. I was told that they charged NATS £50,000 per year for the privilege of seeing a picture which anyone can now bring up for free on the internet!!

<<ATC - You turned and climbed without clearance. I am going to send a report and your stupid captain ass is toast.>>

Thankfully, Air Traffic Controllers are professional people who would never use such language.

Also meant to add something I've said many times.. When I was working the interpretation of patterns on airborne weather radar varied dramatically between types of aircraft and airlines; sometimes even with the same type and same airline. One would continue as if there was no weather whilst the one 3nm behind wanted to gyrate all over the sky.

Well, in my oppinion you must avoid CBs telling ATC your intentions in order that the service providing to the rest of the traffic by ATC is safe and correct. If you can´t contact to ATC, then I wouldn´t wait and I would make my decision, I mean to avoid CBs keeping in mind my TCAS.

I don´t agree to select SQ 7700, It is not a good idea because in that case everyone would be performing a missed approach instructed by ATC as you would be in an urgent situation.

I think the ATC should have given clearance to enter holding pattern until the mess is solved. I don´t understand why ATC allowed that stress situation as there are a lot of IF or IAF inside TMA or even you can say: 360º OVER HERE

If your endurance let you a hold over a point... I would make that decission until weather improves.

BR.