flying in Class E / transition layer question

[RFguy]

I was reading this . So if the upper level of the transition layer is FL115 on the day , can I fly at FL115?

Because, by the definition I am not flying inside the transition layer at FL115 . (FL100 to FL115 in this example)

about as good as it gets with the Archer is about a DA of 11500. 

 

[turboplanner]

1 hour ago, RFguy said:

I was reading this . So if the upper level of the transition layer is FL115 on the day , can I fly at FL115?

Because, by the definition I am not flying inside the transition layer at FL115 . (FL100 to FL115 in this example)

about as good as it gets with the Archer is about a DA of 11500. 

 

Email CASA for a definitive answer.

[old man emu]

If the Transition level was FL115, the area QNH could be as low as 997 hPa, in Australia the weather on the ground would be pretty nasty. Think of the August winds.

 

The transition altitude (TA) is the altitude above sea level at which aircraft change from the use of local barometer derived altitudes to the use of settings based on 1013.5 hPa. When operating at or below the TA, aircraft altimeters are usually set to  (QNH) Above the TA, the aircraft altimeter pressure setting is normally adjusted to the standard pressure setting of 1013.25 hectopascals. The transition layer is the airspace between the transition altitude and the transition level. According to these definitions the transition layer is 0–500 feet  thick.

 

Looking at things from above the transition altitude, an aircraft flying at the 'transition level', in this example FL115, would not have adequate separation from traffic flying on QNH at the transition altitude. Instead, the lowest usable "'flight level'" is the transition level plus 500 ft.

 

Consider the TA to be a line in the sky. Below it, QHN prevails. Above it 1013.25 prevails. The connection between "transition altitude" (TA), "transition layer" (TLYR), and "transition level" (TL) is

TL = TA + TLYR

[RFguy]

But if you are flying at the 10k' TA, you have altimeter QNH = 1013.
(temp effects aside)
If an  aircraft was flying with altimeter set for  1013 and QNH = 1013 , at an indicated 9500' for they are flying at 9500 PA. 
If the aircraft was flying  with altimeter set for  1013 and QNH actual = 997, (IE reads higher than you really are because air pressure is lower)  at an indicated 9500' they are flying at ~ 9500-440'. = ~9060' PA
If the aircraft was flying  with altimeter set for  1013 and QNH actual = 1030, (IE reads lower than you really are)  at an indicated 9500' they are flying at ~ 9500+467'. = ~ 9967' PA
umm is that right ?

[RFguy]

I have emailed CASA . We'll see what I get back. Generally, a 2D defined medium  has boundaries to define it and these are not necessarily inclusive.

 

[KRviator]

You can cruise at the Transition Altitude, or the Transition Level, but not within the Transition Layer.  AIP ENR 1.7.2.1.4

As you've already noted, the layer thickness may vary depending on actual QNH, which will affect whether you can cruise at FL110-FL130, but like, for example, where Class C overlays Class G at 8,500, you can cruise at 8,500 and you're still in G.

[facthunter]

You are supposed to have readjusted your references before you descend out of or climb through the Transition layer. . Within  that piece of sky people will be in various stages of resetting and cross checking so positive separation cannot be  achieved.    Nev

[RFguy]

seems there has been continuous change of this chapter in the AIPs

in 2017  there was a section descibed as "Limitation" .. - and it implied NO to my question -  IE that  you cannot cruise at FL110 if the upper boundary was FL110 for the day.

 

BUT !!!

but not in the 2022/- This has been replaced with TABLE 5 - B

 

Table 5 indicates that FL115 is available  unless QNH < 997
So this is different - ish

 

 

 

Edited June 26, 2023 by RFguy

[turboplanner]

10 minutes ago, RFguy said:

seems there has been continuous change of this chapter in the AIPs

in 2017  there was a section descibed as "Limitation" .. - and it implied NO to my question -  IE that  you cannot cruise at FL110 if the upper boundary was FL110 for the day.

 

BUT !!!

but not in the 2022/- This has been replaced with TABLE 5 - B

 

Table 5 indicates that FL115 is available  unless QNH < 997
So this is different !

 

 

 

That's the real CASA disease; it happens on so many subjects; not an issue if you're flying every week, but a PIA for occasional trips.

[facthunter]

Careful there OR someone may label you a CASA Hater.  Nev

[RFguy]

Change is OK.

The section of the AIP on this (1.7)  from 2017 was a bit of a dogs breakfast. the usual translation from  legislation to plain language. The CASA legislation  is full of "statement followed by a plethorea of exceptions to that statement " !

that's sort of how the previous AIP section was written.

This is better . multiple passes of it and I can be fairly competent of interpreting it as the upper boundary layer (spelt out by the Area QNH)  is NOT part of the transition buffer layer. 
IE if the buffer is FL100 to FL115,  (Area QNH >=997 and < 1013 then you can cruise at FL115.

 

 

 

Edited June 26, 2023 by RFguy

[KRviator]

52 minutes ago, RFguy said:

seems there has been continuous change of this chapter in the AIPs

in 2017  there was a section descibed as "Limitation" .. - and it implied NO to my question -  IE that  you cannot cruise at FL110 if the upper boundary was FL110 for the day.

 

BUT !!!

but not in the 2022/- This has been replaced with TABLE 5 - B

 

Table 5 indicates that FL115 is available  unless QNH < 997
So this is different - ish
 

Could be because they're replaced that chapter with a pretty new graphic in the latest AIP? 

[Kieran17]

The unavailability of FL110 for cruise when the Area QNH is less than 1013 is due to the Transition Layer becoming squished in with the low QNH.

 

If the Area QNH is less than 1013hPa, the vertical distance between A100 and FL110 is less than 1000ft (squished).

If the Area QNH is 1013hPa (1013.25), the vertical distance between A100 and FL110 is 1000ft.

If the Area QNH is Greater than 1013hPa, the vertical distance between A100 and FL110 is greater than 1000ft (fattened).

 

Due to the squishing of the Transition Layer when the QNH is low (Transition Altitude and Transition Level less than 1000ft apart), cruising at FL110 is not available with an Area QNH less than 1013hPa. This squishing continues to happen as the Area QNH lowers, at less than 997hPa, there will be less than 1000ft between A100 and FL115. 

 

Example QNH table below:

For QNH 1013 the Transition Layer is 1000ft thick. The higher the QNH goes, the thicker the Transition Layer becomes: at QNH 1017, the Transition Layer is 1120ft thick.

As the QNH lowers, the Transition Layer becomes compressed, so a 'correction*' is applied. At QNH 1012, there is only 970ft between A100 and FL110, therefore, cruising at FL110 is no longer available and a 500ft 'correction buffer*' is added to the Transition Layer to ensure there is at least 1000ft between A100 and the next available Flight Level (FL115).

The compression continues as the QNH lowers, and at QNH 996, there is 990ft between A100 and FL115, so the next 'correction*' value kicks in, FL115 is no longer available and the next available Flight Level is FL120.

 

 

 

So, on a low QNH day, if the Area QNH is less than 997, cruising at FL115 is not available because there is less than 1000ft between A100 and FL115.

 

 

 

If there were no corrections* applied to the Transition Layer, by the time the QNH reaches 979hPa, altitude A100 would be 20ft above flight level FL110.

 

 

(*not an actual term, but I couldn't think of a better one)

 

QNH	Compression	Correction	Transition Altitude	Layer Thickness	Transition Level
1017	1120	0	A100	1120	FL110
1016	1090	0	A100	1090	FL110
1015	1060	0	A100	1060	FL110
1014	1030	0	A100	1030	FL110
1013	1000	0	A100	1000	FL110
1012	970	+500ft	A100	1470	FL115
1011	940	+500ft	A100	1440	FL115
1010	910	+500ft	A100	1410	FL115
1009	880	+500ft	A100	1380	FL115
1008	850	+500ft	A100	1350	FL115
1007	820	+500ft	A100	1320	FL115
1006	790	+500ft	A100	1290	FL115
1005	760	+500ft	A100	1260	FL115
1004	730	+500ft	A100	1230	FL115
1003	700	+500ft	A100	1200	FL115
1002	670	+500ft	A100	1170	FL115
1001	640	+500ft	A100	1140	FL115
1000	610	+500ft	A100	1110	FL115
999	580	+500ft	A100	1080	FL115
998	550	+500ft	A100	1050	FL115
997	520	+500ft	A100	1020	FL115
996	490	+1000ft	A100	1490	FL120
995	460	+1000ft	A100	1460	FL120
994	430	+1000ft	A100	1430	FL120
993	400	+1000ft	A100	1400	FL120
992	370	+1000ft	A100	1370	FL120
991	340	+1000ft	A100	1340	FL120
990	310	+1000ft	A100	1310	FL120
989	280	+1000ft	A100	1280	FL120
988	250	+1000ft	A100	1250	FL120
987	220	+1000ft	A100	1220	FL120
986	190	+1000ft	A100	1190	FL120
985	160	+1000ft	A100	1160	FL120
984	130	+1000ft	A100	1130	FL120
983	100	+1000ft	A100	1100	FL120
982	70	+1000ft	A100	1070	FL120
981	40	+1000ft	A100	1040	FL120
980	10	+1000ft	A100	1010	FL120

 

Edited June 30, 2023 by Kieran17
Added Transition Level and Altitude to table

[Student Pilot]

On 26/06/2023 at 5:14 AM, RFguy said:

I have emailed CASA . We'll see what I get back. Generally, a 2D defined medium  has boundaries to define it and these are not necessarily inclusive.

 

The only thing you will get back will be a reference for which AIP/Regs to look at. CASA doesn't give definitive answers.

[facthunter]

CASA IF you can understand our latest rules let us know and we will look into it.. A lot of it is LAWYER SPEAK.  and needs' interpretation.. It's ever been thus.  Nev

[RFguy]

It is significant that  at least in the AIP, every couple of years there has been a change of the way they spell it out.. at least 4 times since 2011.....

Now, the most recent AIP, that I think I can interpret with the intention of the text.  But they did change it since 2017, presumably people like me writing in and querying.

 

 

[Kiter]

The last time I flew above 10,000' in an unpressurised aircraft without supplemental oxygen was 1983 in PNG where, if my memory serves the transition level was higher due to there being lots of mountains exceeding 10,000'. I recall my mate saying you weren't allowed to plan to fly above 10,000' without oxygen, but once in the air you could amend plans to do so. I needed to one day and it was common there.

Just had a look at the Part 91 MOS and my interpretation is no need for oxygen as long as the cabin pressure does not exceed FL 125 for more than 30 minutes. Did I miss anything?

[RFguy]

MOS26.43 Supplemental oxygen (MOS 26.43) An aircraft must carry sufficient supplemental oxygen as described in Table 25. Fitted or carried supplemental oxygen, must be able to be stored and dispensed to the crew and passengers. Flight crew members must use supplemental oxygen in accordance with the supply requirements set out in Table 25.

 

 

 

[facthunter]

US has a different level for 02 to us here. Their's is 2000ft higher. How it affects you depends on age, fitness and being used to altitude. 65 t0 69 I regularly flew to Lae from POM on a DC4 which had oxygen  available. to crew.  The LSALT on the way back is 17,400 and I can't recall anyone using the masks but I once was asked by a medico why My red cell count was so high and apparently it was to do with flying unpressurised.  Nev