Patrick wrote:
But frankly, there is a subjective element to this as well – for those flying along even more so.
Fully agree – but then we are talking psychology. Psychologically you are absolutely right that the majority of people (unfortunately) have a reverse confirmation bias when it comes to “near misses” (not only in aviation):
After a car accident one “survives” unharmed most people have some form of increased fear against driving a car – even though facts should have just taught them that driving is so safe that even in the unlikely event of an accident odds are very high that they walk away unharmed. But with most people psychology turns that around. Same effect in aviation: Pilots who use a traffic system for the first time are likely to start feeling less secure because all of the sudden they see lots of dots on their traffic system instead of taking the facts as facts realizing that obviously w/o the TAS the traffic has also been there but obviously it is not as dangerous as thought.
Psychologically, however, I would argue that especially for those “flying along” it is much more comforting to know “we have rules that make sure that another plane in opposite direction is not in the same height as we are” than “we are all flying randomly so that mathematically the odds are low that we meet”.
Therefore especially from a psychological point of view flight level rules are a good thing!
I think one might bear in mind why the introduction of IFR became so urgent in the first place.IIRC there were two passenger aircraft on scheduled flights in the USA.
It was not a particularly bad day weatherwise, although there was some cloud around.
Air travel was VFR and would fly at whatever altitudes they thought best.
Airline travel was a bit of a luxury back then and crews would try to give their high paying passengers, a little extra.
On this particular day, 2 airliners decided to just take a short detour from their route to give the passengers a view of a well known beauty spot IIRC it was the Grand Canyon. The trouble was they arrived there at the same time at the same altitude. Many people died that day and it was to lead to things like the semi-circular rule and later to the IFR system.
Over the years the rules that came from that fateful day have made air travel one of the safest forms of transport today. IMO one should think very carefully before unilateral or even forumlateral decisions to go against International norms and recommended practices.
Alpha_Floor wrote:
Say we’re flying westerly, the TA is 6000ft and the TRL is FL70. Because you can’t fly inside the transition layer, that leaves effectively only 4500ft and FL85 as usable VFR cruising levels. The difference is 4000ft. And anyway, you may not want to be able to fly as high as FL85 but 4500 is too low for comfort/weather/views/reasons.
TA and TRL are linked to an airport, so you are in CAS. ATC clears you to whatver altitude they choose. It’s not uncommon to be cleared to a whole thousand feet (no +500ft) to ease separation. VFR flights are assumed to be amateur pilots with barely a paper map and little skills to hand-fly +/-200ft.
OCAS, 3000ft AGL is both TA and TRL, there is no layer you can use the FL65 as well. It helps if everyone sticks to the system. Several times I have flown by other planes that I did not see until the last seconds or did not get info about because the freq was very busy, but we were at the altitude we were supposed to so it was a non—event.
Arne wrote:
TA and TRL are linked to an airport, so you are in CAS
That is not correct. In Belgium, the TA is valid for the whole FIR and you need to fly FL above the transition layer.
airways wrote:
the TA is valid for the whole FIRTA can be fixed (it’s written on the plates or in the AIP), TRL cannot (it’s in the ATIS). Do you have a daily FIR TRL, or a 0ft layer? Either way, all levels every 2000ft are available, not just 45 and 85.
Arne wrote:
TA and TRL are linked to an airport, so you are in CAS.
Not necessarily CAS. You have airports with TA and TL in uncontrolled airspace as well.
OCAS, 3000ft AGL is both TA and TRL, there is no layer you can use the FL65 as well. It helps if everyone sticks to the system. Several times I have flown by other planes that I did not see until the last seconds or did not get info about because the freq was very busy, but we were at the altitude we were supposed to so it was a non—event.
That’s not so. The relevant rule in SERA is:
SERA.3110 Cruising levels
The cruising levels at which a flight or a portion of a flight is to be conducted shall be in terms of:
(a) flight levels, for flights at or above the lowest usable flight level or, where applicable, above the transition altitude;
(b) altitudes, for flights below the lowest usable flight level or, where applicable, at or below the transition altitude
Note that there is no mention of 3000 ft. There used to be a “default” TA of 3000 ft AGL for VFR OCAS, but hasn’t been at least since SERA was introduced in december 2014.
Also note that there is no mention of a transition level or transition layer in SERA.3110. As you say, there is usually no TL OCAS so the concept of transition layer is really only relevant in CAS where ATC has to separate traffic. If a TA has been defined OCAS, nothing prevents you from flying level inside what would have been the transition layer in CAS – but then you should fly at flight levels.
The Swedish authority initially made the unfortunate interpretation that where no transition altitude applies, altitudes should be used up to FL95, as that is the base of controlled airspace in Sweden outside TMAs. That lead to a lot of ambiguities and other problems so they thought better of it and today all of Sweden FIR is declared to have a TA of 5000 feet – except in the mountains where the TA is either defined for an airport or is 3000’ AGL. (Ref. TSFS 2020:59, chapter 2, §§7-8.) Other countries will have their own definitions of TA OCAS – or none.
So if the QNH is e.g. 1000 hPa, you can fly eastbound at FL55 in Sweden FIR, which corresponds to approximately 5150 ft on QNH.
That also means that in Sweden FIR you should fly VFR westbound OCAS at 4500’ – not FL45 unless the QNH is above 1032 (which is unusual) in which case you can choose between 4500’ and FL45.
Alpha_Floor wrote:
My personal opinion is that this whole thing makes all the sense in the world for IFR traffic but very little sense for VFR…
In wide open large chunks of uncontrolled airspace, clear blue sky, it makes sense IMO, because then you know what to expect from others, and others know what to expect from you. However, add in some clouds, terrain, TMAs and other controlled airspaces, and the system is rendered a bit irrelevant.
For instance, just an example, flying from Sandane (ENSD) back home (ENVA) is a 165 NM trip in NE direction. Due to terrain, the lowest possible altitude will be 9500 feet. But at that altitude, you will fly in G airspace for 30 something NMs only. The rest is in TMA and Polaris. If you chose to fly along the coast, which is a bit longer, but often preferable due to weather, then even using the min 3500 feet over water, you are flying in TMAs all the time. No matter how you fly, the system is rendered irrelevant most of the time, or all of the time.
Ibra wrote:
Curious question, was there any documented VFR mid-air collision in uncontrolled airspace above 4000ft agl worldwide? in VMC? in IMC?
There is the 1997 Namibia mid-air collision (in VMC) where a Tu154M and a C-141 collided over the Atlantic Ocean. The accident report explicitly blamed the Tupolev’s crew for not flying the semi circular rule.
The two RAF Grob aircraft which collided a few years ago happened at 4500ft, IIRC, but they were not unrelated flights; they were in a loose formation. That event led to a UK avionics shop, Lees Avionics, getting a Ministry of Defence contract for equipping all the Grobs with a TAS605 and a SN3500 EHSI on which to display the traffic.
The UK has not had an IMC mid-air since c. WW2. VMC ones, 1-2 year, and mostly near airfields.
Clipperstorch wrote:
There is the 1997 Namibia mid-air collision (in VMC) where a Tu154M and a C-141 collided over the Atlantic Ocean
At 35000ft that looks like IFR in controlled airspace or under ATC watch in procedural IFR routes?
Still it’s MAC middle of +/-5NM airway probably pre-GPS days rather than loss of seperation…
https://en.wikipedia.org/wiki/Mid-air_collision#List_of_notable_civilian_mid-air_collisions
Most of MACs documented above are IFR on 30kft cruise, or approach/climb, or against very low level VFR
gallois wrote:
On this particular day, 2 airliners decided to just take a short detour from their route to give the passengers a view of a well known beauty spot IIRC it was the Grand Canyon
For my list above of MACs, this one fits “VFR free-style MAC description”, two VFR hitting each other at 3700ft !
One traffic cancelled IFR and went for low VFR on a tour flight
https://en.wikipedia.org/wiki/Proteus_Airlines_Flight_706
There was one in the Hudson which was low 2*VFR on tour as well
Not sure if flying VFR to view the best spot is very related to “VFR in cruise question”
