US has a 18,000 ft transition altitude while Europe has transition altitude of 3000-6000 ft. When flying in US airspace, given the high altitude at 18,000ft,  wouldn't approach be more difficult , due to steep descent?  

Historical reasons mostly. There is an initiative to adopt the USA model in Europe too.

In fact, looking back, the ICAO flight level concept itself only dates back to the 1970s, so the whole issue is under 50 years old in its modern sense.

The airspace systems around the world developed differently over time.  For a long time, many States use QFE altimeter settings for takeoffs and landings, and then transition to QNH enroute.   Only at high altitudes in the US was QNE used

With QFE, the altimeters in the aircraft read zero feet on the runway.  American and Eastern used QFE for many years, and this is reflected in the Level D's B767 model by the very large altimeter in the standby instrument stack.  Dispatch would send QFE altimeter settings to the crew on arrival and prior to departure.  Each of the pilot's primary altimeters would be set to QFE, but the center altimeter would be set to QNH, or sea level altimeter setting used to fly altitudes issued by ATC.  Eastern used QFE up to its demise in the early 1990s.  American ceased using QFE after an accident in Bradley involving a MD80 on approach and because of the transition to all glass cockpits around 2000.

in the Transition altitude used by higher, at 24,000.  However, in the 1960 it was lowered to 18,000 as more jet traffic proliferated.  Faster speeds of jets likely caused the change since ATC would have to issue new altimeter settings every 100 NM per the regulations under IFR.  That's every 15 minutes at average cruise speeds. It was just easier using QNE. 

A few years ago there was a push to raise Europe's transition altitude to a uniform 18,000 ft. Not sure what happened to it.

Rich 

Edited July 15, 20205 yr by richjb2

On 7/15/2020 at 10:02 PM, Ilari Kousa said:

In fact, looking back, the ICAO flight level concept itself only dates back to the 1970s, so the whole issue is under 50 years old in its modern sense.

Thanks

On 7/15/2020 at 10:08 PM, richjb2 said:

The airspace systems around the world developed differently over time.  For a long time, many States use QFE altimeter settings for takeoffs and landings, and then transition to QNH enroute.   Only at high altitudes in the US was QNE used

 

Rich 

I need some help on the altitude program in FMC. This flight is from VHHH to WSSS and has crossed the 18,000ft transition level, currently the plane is at waypoint EPDOS, according to the FMC, the plane should be flying at 36,000 ft, but why the plane stay at 25,000 ft? The plane is in VNAV and LNAV mode, and CMD A is activated, doesn't the FMC control the plane altitude? 

Secondly, while the plane is at waypoint EPDOS, why 250/FL210B is highlighted in magenta?

 

Here is the screenshot link of the cockpit, many thanks in advance.

https://imgur.com/HtxL54m

Edited July 17, 20205 yr by Billcoke
typo error

Billcoke,

Your plane is at FL250 simply because on the MCP (Autopilot), your altitude is set at 25000. The plane wont climb any higher until you set a higher altitude on the MCP. You need to set the MCP to 36000 if you want the plane to climb to that altitude (and use either FLCH or reset VNAV for the climb to resume.

At waypoint PIBAP, you see 250/FL250B in magenta because it is the next speed/altitude restriction that you must comply with on your route. It means that you must cross PIBAP at a speed of 250 KIAS and an altitude of FL250 or below. The magenta color differentiate a compulsory restriction from a normal profile calculation (in light grey).

The cruising altitude you initially entered in the FMC (FL360) during the preparartion of your flight is used by VNAV to calculate the climb profile, while the altitude set on the MCP is what the aircraft will actually climb to. 

 

 

On 7/15/2020 at 1:08 PM, Billcoke said:

US has a 18,000 ft transition altitude while Europe has transition altitude of 3000-6000 ft. When flying in US airspace, given the high altitude at 18,000ft,  wouldn't approach be more difficult , due to steep descent?  

To ensure terrain clearance the transition altitude must be higher than the highest terrain in the area covered. The USA has a national transition altitude policy and 18,000 feet satisfies this. European countries operate their own policies, and many have regional differences for TA. Regional TA can therefore much lower than would be needed in mountainous areas. Whether it should be is another matter.

Making TA higher doesn't make descent any steeper. Flying in Europe it's easy to associate resetting the altimeter with beginning approach, but that's just a coincidence.

Edited July 28, 20205 yr by kevinh

On 7/19/2020 at 7:30 AM, NBouc said:

Billcoke,

Your plane is at FL250 simply because on the MCP (Autopilot), your altitude is set at 25000. The plane wont climb any higher until you set a higher altitude on the MCP. You need to set the MCP to 36000 if you want the plane to climb to that altitude (and use either FLCH or reset VNAV for the climb to resume.

At waypoint PIBAP, you see 250/FL250B in magenta because it is the next speed/altitude restriction that you must comply with on your route. It means that you must cross PIBAP at a speed of 250 KIAS and an altitude of FL250 or below. The magenta color differentiate a compulsory restriction from a normal profile calculation (in light grey).

The cruising altitude you initially entered in the FMC (FL360) during the preparartion of your flight is used by VNAV to calculate the climb profile, while the altitude set on the MCP is what the aircraft will actually climb to. 

 

 

Many thanks, in other words, the 250/FL250B in magenta is to remind pilots of the next restriction.

 

Edited July 29, 20205 yr by Billcoke
typo error

To add even more confusion, China and Mongolia are two of the last hold outs for requiring flight levels in meters versus feet. Not sure WHY that is, but it must be annoying flying over either country and having to do conversions.