Base of N864 at REXAM

[NorthSouth]

Anyone know why the base of the section of N864 containing REXAM is defined as an altitude (4500ft) rather than a flight level? Surely the transition altitude here is 3000ft?

NS

[stillin1]

I must be really bored today!
Rexham, on my chart is on A25 and is toted as having a base of 45 FL60.:confused:

[swp53]

Stillin1

Your charts are out of date ?
The airways were redesignated in early 2004 if my memory is correct? Mind you I can remember when the Alphas and Golfs etc were Ambers and Greens etc.
No idea about the original question of base of airway.

Regards,
Steve.

[PA28pilot]

NorthSouth

Not 100% sure but I believe this section of the airway is controlled by Manchester, where the Transition Altitude is 5000'.

Regards
PA28pilot

[Ops and Mops]

Off the top of my head, it could be that the base of the airway is lowered to assist descent into the Mancheter TMA , inside which the Transition Altitude is 5,000ft. I believe REXAM is also used for EGCC STARS.

The base of some of the lower airways are also defined as an altitude as well as a Flight Level for use when the QNH/RPS is lower than 1013.2. The altitude is given to show the lowest possible level of the base of the airway (i.e FL45 would be lower than 4500ft and possibly not terrain safe.)

Hope that makes sense..........:bored:

[NorthSouth]

pa28pilot/ops&mops:
Thanks, you've got it - AIP shows N864 btwn WAL and MONTY is indeed controlled by Manch hence traffic in it is operating on the Manch QNH when below 5000ft.

This has the rather odd implication that any traffic flying underneath this bit of N864 also ought to have the Manchester QNH set, even though N864 is not part of the Manch TMA.

NS

[stillin1]

You are right - chart is out of date - picked up an old one in the study OOps:\

[DFC]

This has nothing to do with who controls the traffic within the airspace.

The rules as far as I am aware are that pilots in Class G use the appropriate aerodrome QNH when flying in or under an associated TMA/CTA and at or below the transition altitude.

Since this is an airway base and is defined as an altitude, by definition the transition altitude in that place must be at or above the base. Otherwise it would be defined as a flight level.

Taking the two above points into account then as far as I am aware the base of the airway would be defined using the appropriate Regional Pressure Setting so that pilots in the Class G airspace below the airway could remain below the base.

Where airways are defined as a Flight Level and there is also published a minimum altitude, this basically tells us that the base of the airways is FLxx but it will never be lower than xxx feet amsl.......this can be required to ensure that a) the FL never goes below the transition altitude (unusual) or below the terrain safe level or below some altitude that operators in class G use for say gliding or getting to the Channel islands etc.

Perhaps this is another example of why we should get rid of regional pressure settings.

Regards,

DFC

[Spitoon]

DFC, it may be an argument to have a common single Transition Altitude - which is coming for Europe anyway.

I don't see why it is any reason to do away with RPS - RPS is essential for flights operating low down outside CAS.

Don't forget that there are one or two aircraft flying around which don't use airways.

[DFC]

Spitoon,

I don't see why it is any reason to do away with RPS - RPS is essential for flights operating low down outside CAS.

Don't forget that there are one or two aircraft flying around which don't use airways.

This has alot to do with Regional Pressure setting.

If the Base is 4500ft on the RPS of say 993 and Manchester ATC put an aircraft along the airway at 5000ft on the Manchester QNH of say 1003 then the departing aircraft will be only 200 feet above the base and an aircraft passing beneath the airway.

Remember that the RPS is the lowest "forecast" pressure for the whole region and a 10mb difference between actual QNH and RPS at opposite ends of the region is not unheard of.

Again it is important to remember that the Monty SID stops at 5000ft on the Manch QNH......the above close encounter is set up in the system should the aircraft radiofail or ATC be unable to get some climb on (v. unusual).

This is probably one of the many errors in the system that nobody has noticed before!

Regards,

DFC

[Spitoon]

My point was that all those pilots flying around low down outside CAS need something to base their terrain clearance assurance on. The RPS does this.

Don't try and take away such a valuable tool from pilots outside CAS because there is a flaw in the ATC system. Fix the ATC system.This is probably one of the many errors in the system that nobody has noticed before!Have you raised your concerns with the agency that uses the procedure? Have you raised the general concern with the CAA?

I can't speak for Manchester but I can assure that I am fully aware of this potential and allocate levels which take account of any erosion of airspace protection .... just as I am fully aware of all of 'errors' in the system when operating around the Transition Layer.

[chiglet]

A line [almost] KEGUN-RISLA A3000
[approx] midway REXAM-MONTY A4500
MONTY FL85
10S MONTY FL105
10S NITON FL125
RADNO FL105
From MONTY south, between 200-0700 base is FL65
hope this helps
watp,iktch

[PPRuNe Radar]

If the Base is 4500ft on the RPS of say 993 and Manchester ATC put an aircraft along the airway at 5000ft on the Manchester QNH of say 1003 then the departing aircraft will be only 200 feet above the base and an aircraft passing beneath the airway.

You are absolutely right DFC. Manchester should in theory tell the pilot to change to the RPS as he leaves the boundary of their TMA. Even more interesting are the Liverpool SIDs which terminate at 4000' and will leave CAS just after DOGIT if not given climb whilst on the way to REXAM.

However I expect someone from Manch can probably tell us how it is dealt with in real life.

[NorthSouth]

Well this has turned out to be much less boring than I expected!

Consider this:

(1) PPrune Radar, you suggest that Manch SID tfc should be on the RPS, but why should anything UNDERNEATH be on the RPS? It's not under a TMA or CTA so surely if above 3000ft they must be on 1013 if IFR (with MSA here 3100ft), and should be if VFR?

(2) To add to the confusion, Hawarden's 05 procedures go through here at 3100ft on the Hawarden QNH so whatever you have on your altimeter you might well meet a Beluga going the other way.

NS

[PPRuNe Radar]

(1) PPrune Radar, you suggest that Manch SID tfc should be on the RPS, but why should anything UNDERNEATH be on the RPS? It's not under a TMA or CTA so surely if above 3000ft they must be on 1013 if IFR (with MSA here 3100ft), and should be if VFR?

Mmmm, so if they have 1013 set and the base is defined as an altitude and not a Flight Level ... how do they know they are below the base ??

And taking your argument to its logical conclusion, shouldn't SIDs which terminate outside the TMA therefore also go to a Flight Level and not an altitude ?? :p

It's an example of where the 'rules' don't match up, something not uncommon in the UK.

[NorthSouth]

Just to prove how sad I am I have checked through AIP ENR for any other examples of this and find that it seems to be a phenomenon peculiar to the margins of the Manchester TMA - take a look at N57 (formerly A2) in the Blackburn-Burnley area, plus the airspace west of Wallasey and between Huddersfield and Sheffield. There seems to be nowhere else in the UK where airways (other than those passing through TMAs) have a base which is not a flight level.

NS

[DFC]

North South,

Since the base is defined as an altitude then the transition altitude must be at or above that level otherwise, it would be defined as a flight level.

Since the base of the airway is at or below the transition altitude, the quadrantal rule does not apply. Thus a NW bound flight in class G at say FL45 would have to adjust to a convenient altltiude (4000 QNH) to pass beneath the airway and than back to FL45 once clear. Some use 4400 QNH but the Airprox Board report into a recent airspace infringement recomended 500ft below the base if possible.

Other pilots would probably plan a track further to the south and take advantage ot the high airway base during the day.

As for Hawarden- that is an airfield in Class G and has nothing to do with controlled airspace. It should be treated the same as Oxford, Gloucester, Filton etc - stay well clear unless VMC or in receipt of an appropriate service.

---
PPRUNE Radar,

It is entirely possible to stay below the base while still using 1013 just as we can fly at a FL that is terrain safe over Snowdon where the TA is 3000ft but the mountain extends above that altitude. The same procedure but from the opposite direction!

However, as far as I am aware the rules (and common sense) dictate that pilots underflying anything defined as an altitude should use an altitude to ensure segregation (not separation).

As for the R/T failure procedures - the UK AIP warns pilots that using the R/T failure procedures may take them outside controlled airspace and this is true on most SIDS including those of EGLL. But it seems to me that this base was put there to protect late climbing departres from EGCC and EGGP - something it does not really do!

Regards,

DFC