Has there been a push by ICAO or industry bodies to switch flight level to metric units? Besides intertia (since commercial aviation started in the US and US standards became the norm), what are the other factors that prevent a metric flight level standard from being implemented?

If a metric standard is adopted, what is the proper granularity/increment values for flight level values that result in enough vertical separation? Obviously, a hard conversion from FL350 to FL10650 would create a mess (Metric flight-level table: https://i.imgur.com/1W3Juve.jpg).

My core question is this: if a metric stardard is adopted, what is the increment step values for metric FL values? (taking into account safety margins, usability, readability, etc.)

Here is an example (with the last two zeros dropped, so FL020m really means 2000 meters):

- FL020m (6561 feet)
- FL022m (7217 feet)
- FL022m (7874 feet)
- ...
- FL098m (32152 feet)
- FL100m (32808 feet)
- FL102m (33464 feet)

Looking at the above increment values (of 200 meters), the vertical separation would be 656 feet.
Alternately, if increments of 250 meters is used, vertical separation would be 820 feet.
Alternately, if increments of 300 meters is used, vertical separation would be 984 feet.
Alternately, if increments of 400 meters is used, vertical separation would be 1312 feet.

The most convenient increment appears to be 200 meters, because it does not require extra thinking: 200, 400, 600, 800, ... , 9800, 10000, 10200
The 250 meter increment is good due to predictability: 250, 500, 750, 1000, ... , 9750, 10000, 10250 (the drawback is we could only drop one zero, rather than two)
The 300 meter increment is awkward, because we would have to think about some odd digits: 300, 600, 900, 1200, ... , 9900, 10200, 10500
The 400 meter increment is slightly awkward, because we have to think about divisibility by 400: 400, 800, 1200, ... , 9600, 10000, 10400

Some observations/comments: (a) vertical separation of 300 meters is pretty darn close to what we have now (984 feet instead of 1000 feet); (b) vertical separation of 200 meters creates capacity in existing space; (c) vertical separtion of 400 meters takes away capacity in existing space. I know that China has it's own weird way of doing things (https://en.wikipedia.org/wiki/Flight_level#People's_Republic_of_China), with increments of 600 meters, which seems wasteful.


Here is a classical altimeter, shown for fun:

If it ain't broke, don't fix it, right?

I'll admit, obviously I'm used to the empirical system. But has that caused any problems other than the Gimli Glider? And even there, protocol in place for the normal conversion wasn't used.
All pilots use knots (nautical miles per hour) for speed and nautical miles to measure distance, which aren't native to either metric or empirical systems, and even American pilots don't have problems with that, to my knowledge. After all, it almost doesn't matter what unit is used. ATC gives instruction with simply a number, and the pilots read or change the systems, which focus on just the number, not the unit.

BWIAirport wrote:

If it ain't broke, don't fix it, right?

I'll admit, obviously I'm used to the empirical system. But has that caused any problems other than the Gimli Glider? And even there, protocol in place for the normal conversion wasn't used.
All pilots use knots (nautical miles per hour) for speed and nautical miles to measure distance, which aren't native to either metric or empirical systems, and even American pilots don't have problems with that, to my knowledge. After all, it almost doesn't matter what unit is used. ATC gives instruction with simply a number, and the pilots read or change the systems, which focus on just the number, not the unit.

I love your answer. Thanks.

There is no chance that this will ever happen, not in the US anyway. I would be surprised if we ever switched to using the word "decimal", much less changing the numbers for altitude stratums.

I've always wondered: why the continued use of knots? I can understand the argument for wanting to change to metric, though the "If it ain't broke" argument fits perfectly here, but why are speeds and distances still done in knots? Can someone point me to an explanation as to why or is it all tied in to its use by ships first and then adapted by early aviation and it was never shifted over? It just seems like one more chance for confusion and few in the public realm use knots.
I've been waiting for a thread that would let me ask this.
Thanks

ClipperYankee wrote:

I've always wondered: why the continued use of knots? I can understand the argument for wanting to change to metric, though the "If it ain't broke" argument fits perfectly here, but why are speeds and distances still done in knots? Can someone point me to an explanation as to why or is it all tied in to its use by ships first and then adapted by early aviation and it was never shifted over? It just seems like one more chance for confusion and few in the public realm use knots.
I've been waiting for a thread that would let me ask this.
Thanks

https://www.quora.com/Why-is-the-speed- ... ph-or-km-h
This article may be of help. It seems it was derived from degrees of latitute.
As for being a chance for confusion, pilots grow up around knots and it is likely secondhand to them at the point they actually enter a cockpit. I have never flown a plane aside from Microsoft Flight Simulator, and I even instinctively think of airspeed in knots and nothing else. Worst case scenario, knots and mph are close enough that an error shouldn't be too problematic (140kn=161mph). Although, since all a pilot's information comes from the airspeed indicator on the aircraft, which is already in knots, there's really no space for a conversion error to be made.

GalaxyFlyer wrote:

[..] The Chinese spacing at low levels is not 600m, it’s 300m between opposite directions. At F291, the actual spacing is not 300m but a odd number that is rounded up to create 1,000’ spacing. Crews use 291, 301, 311 to have 1,000’ but the assigned level is in metrics. [..]

Do US pilots that fly into mainland Chinese air space need some kind of supplemental certification or supplemental type rating? Do UA / DL / AA / HA aircraft that fly into Chinese airspace receive software upgrades to input metric numbers? Or is the computation done in pilots' heads?

brian415 wrote:

Do US pilots that fly into mainland Chinese air space need some kind of supplemental certification or supplemental type rating? Do UA / DL / AA / HA aircraft that fly into Chinese airspace receive software upgrades to input metric numbers? Or is the computation done in pilots' heads?

HA pilots underwent special "China" training before PEK service commenced and at the completion of training, the pilot was China "certified." This included the new procedures for the conversion of altitude assignments given meters to be converted for feet. All it really involves is consulting a chart to convert the meters to feet. The 330 and I'm sure other modern airliners have the option to set the altitude in meters. The altitude in meters is displayed as a small number on the PFD, while the FCP remains in feet. I'm sure the other carriers had similar training.

brian415 wrote:

GalaxyFlyer wrote:

[..] The Chinese spacing at low levels is not 600m, it’s 300m between opposite directions. At F291, the actual spacing is not 300m but a odd number that is rounded up to create 1,000’ spacing. Crews use 291, 301, 311 to have 1,000’ but the assigned level is in metrics. [..]

Do US pilots that fly into mainland Chinese air space need some kind of supplemental certification or supplemental type rating? Do UA / DL / AA / HA aircraft that fly into Chinese airspace receive software upgrades to input metric numbers? Or is the computation done in pilots' heads?

We don't get any extra training, unless you count being familiar with what's in the ops manual. When assigned a metric flight level, we convert to the level in feet as per the conversion table found in QRH and/or EFB, set that and cross check.

No need for a software upgrade. AFAIK most airliners have a "metric altimetry" button that displays the altitude in meters on the PFD.

Pic shows a 737 PFD. Note the metric altitude top right.

Google China RVSM and you should see an IFALPA briefing bulletin that describes the Chinese FLAS, or Flight Level Allocation Scheme. Excellent reference resource. If u=you happen to be in an old school 767 for instance, this can almost double your workload the 1st time you use it.

Sorry, I skipped over that one. To many metric FL;s spinning around in m head!

Once something becomes a standard, it really no longer makes sense changing it.

BWIAirport wrote:

I'll admit, obviously I'm used to the empirical system.

An empirical system for flight levels -- now that would put the thrill back in flying.

hivue wrote:

BWIAirport wrote:

I'll admit, obviously I'm used to the empirical system.

An empirical system for flight levels -- now that would put the thrill back in flying.

I could have sworn that was right! I of course meant Imperial.

The problem with metric levels is you end up using hundreds, which just feels so much less intuitive than thousands.

speedbird52 wrote:

The problem with metric levels is you end up using hundreds, which just feels so much less intuitive than thousands.

Nailed it.

atcsundevil wrote:

There is no chance that this will ever happen, not in the US anyway. I would be surprised if we ever switched to using the word "decimal", much less changing the numbers for altitude stratums.

It's bad enough they switched over to "Line up and wait." That's something you do at Walmart, not in an airplane...

Moose135 wrote:

atcsundevil wrote:

There is no chance that this will ever happen, not in the US anyway. I would be surprised if we ever switched to using the word "decimal", much less changing the numbers for altitude stratums.

It's bad enough they switched over to "Line up and wait." That's something you do at Walmart, not in an airplane...

Yeah, I know a lot of tower guys had a rough month when that change went in place (Oct. 2011, I think). Phoenix Tower put up signs everywhere that said, "Line up and woof" as a reminder. I'm in a center, and I can promise you that any proposed change to flight levels will be met with strong resistance. I've never even heard of it being an issue, so I'm willing to bet it's not even up for discussion (nor should it be). If it ain't broke, don't fix it.

Moose135 wrote:

It's bad enough they switched over to "Line up and wait." That's something you do at Walmart, not in an airplane...

Actually it's quite useful. If you're using runways for separate ops (see 18/25 on EDDF, or 29/33 on EPWA), it allows you to properly sequence departures (after previous departure you give "line up and wait", then landing clearance goes, once landing is in clear zone, you give departure clearance and off he goes, not having to line up and turn first). It saves some 10-15secs on departure, and in turn allows to increase traffic rate. 12 departures every hour saves a couple of minutes (or allows extra departures).

Cheers,
Adam

gloom wrote:

Moose135 wrote:

It's bad enough they switched over to "Line up and wait." That's something you do at Walmart, not in an airplane...

Actually it's quite useful. If you're using runways for separate ops (see 18/25 on EDDF, or 29/33 on EPWA), it allows you to properly sequence departures (after previous departure you give "line up and wait", then landing clearance goes, once landing is in clear zone, you give departure clearance and off he goes, not having to line up and turn first). It saves some 10-15secs on departure, and in turn allows to increase traffic rate. 12 departures every hour saves a couple of minutes (or allows extra departures).

Cheers,
Adam

Yes, I'm sure he knows that.

What he is referring to is the old 'taxi into position and hold' superceded by the ICAO 'line up and wait'.

This is one of those areas where a specialized language has a ton of momentum. I don't see it going metric at any point in the next century.

And that's even as someone who grew up and thinks of everything in metric. As someone noted, after some point you're more focused on the number, not the unit. It's all about the context.

SAAFNAV wrote:

Yes, I'm sure he knows that.

What he is referring to is the old 'taxi into position and hold' superceded by the ICAO 'line up and wait'.

Aaahhh, right, got that one.
Sometimes there's more to it than I know. Everyone's aware of old takeoff vs departure, but some things just come in automatically when your training was quite...late and you never know if it's superceding any previous phrasing. It's just the way it is.

Thanks for clarification.

Cheers, Adam

masi1157 wrote:

speedbird52 wrote:

The problem with metric levels is you end up using hundreds, which just feels so much less intuitive than thousands.

Imagine one day they might change the flight level spacing to less than 1000ft. What would then be so intuitive with 1000s compared to multiples of 100?

Btw: Imperial units are completely not intuitive at all for the large majority in this world, especially those not in the aviation industry (which I am, still I use SI units for virtually everything except those few aviation exceptions).


Gruß, masi1157

Actually even modest change in level separation, from existing 2000/1000' (610/305m) to 500/250m (1640/820') can give some extra flight levels and become a good enough argument for some areas to switch. And I assume it can happen at existing technology level, without major breakthroughs.
Those could be communicated as, for example, "ten and three quarters" for 10750m (35246') - no chance for confusion.
But the benefit may not be as great to justify conversion.

Why don't we study the areas of the world that do have metric flight levels? AFAIK Russia changed it above a certain altitude. Was this to facilitate traffic not familiar with the metric system?

I am not aware of ICAO pushing for metric flight levels, there has been some discussion to implement geometric levels, it fly the levels the GPS computes to get around altimeter errors.

Problem with metric is where is joins normal levels it consumes two levels as the required separation is not there.

GalaxyFlyer wrote:

Kalvado,

You need to understand the contingency procedures that 1,000’ spacing allows that 500’ would not allow. 500’ spacing (300’ in some contingencies) is the emergency spacing to navigate out of some types of airspace. 500’ spacing is also the default IFR/VFR separation. We don’t need to reduce it any more than the current 1000’.

There’s also the wake turbulence issue that RVSM has introduced.

GF

20 years ago someone could say " 2000' is good, we don't need to go any further". I don't quite believe we're at the end of evolution.
And we're not talking about reduction in half, it is about 20% difference that would make metric work smoothly.