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What Is FL370?  
User currently offlineSIA_B777 From United States of America, joined Apr 2001, 469 posts, RR: 1
Posted (13 years 4 months 5 days 7 hours ago) and read 7716 times:

Sometimes I hear people in this forum talk about FL370.

What does it mean?

23 replies: All unread, jump to last
 
User currently offlineHawaiian717 From United States of America, joined May 1999, 3195 posts, RR: 7
Reply 1, posted (13 years 4 months 5 days 6 hours ago) and read 7666 times:

It means an aircraft is flying at Flight Level 370, or 37,000 feet.

David / SAN


User currently offlineSIA_B777 From United States of America, joined Apr 2001, 469 posts, RR: 1
Reply 2, posted (13 years 4 months 5 days 6 hours ago) and read 7644 times:

Thanks! Smile

User currently offlineMegatop747-412 From New Zealand, joined Sep 2000, 264 posts, RR: 0
Reply 3, posted (13 years 4 months 5 days 6 hours ago) and read 7629 times:

SIA_B777

Just to add on to Hawaiian717's note, FL (or flight level) is the term used to denote the altitude above a certain number of feet - I think it is used to descript alt >10,000 feet. Basically, the FL number is the feet minus the last 2 zeros - e.g. FL310 would be 31,000ft...


User currently offlineBen88 From United States of America, joined Dec 1999, 1093 posts, RR: 2
Reply 4, posted (13 years 4 months 5 days 3 hours ago) and read 7602 times:

I believe FL is used at 16,000 feet and above.

User currently offlineRhodan From , joined Dec 1969, posts, RR:
Reply 5, posted (13 years 4 months 5 days 3 hours ago) and read 7592 times:

FL370 means, flightlevel 370, 37.000 feet.
Where feet indication ends and flightlevel indication starts, depends on the transition level, which is different in each country and by each airport.
In Amsterdam they have i think the transitionslevel 40, in vienna they have normally transitionlevel 60. It also depends on the local QNH. When the QNH is below 1013Hpa, the transiton level will be higher than normal by 10.


User currently offlineJoona From Finland, joined May 2001, 1038 posts, RR: 9
Reply 6, posted (13 years 4 months 5 days 2 hours ago) and read 7589 times:

As mentioned above, FL370 means Flight Level 370 and 37000 feet.

There are altitudes and Flight Levels. Then what makes them different? Well, altitude is below and FL is above, but how to know when it changes? Easy: when you go up, altitude changes to Flight Level at Transition Altitude (TA) and when going down, FL changes to altitude at Transition Level (TL). In Finland TA is always 5000ft and TL is FL45-FL65 depending on the QNH. The "standard" TL in Finland is FL55. In the US, TA is always 18000ft.

Just to let you understand this:

1) You are told to climb FL70, TA is 8000ft. Is this possible?

2) You are told to descend to FL55 with TL being 50, possible?

3) Climb 7000ft with TA at 18000ft. Possible?

4) Descend 4000ft, TL 35, possible?

5) Descend FL60, TL 55, possible?

Now think of these questions and see if you can answer them. I have told you everything you need to know.

Joona  Smokin cool



1740 days idle. Beat that.
User currently offlineJulien.M From Belgium, joined Mar 2000, 143 posts, RR: 0
Reply 7, posted (13 years 4 months 5 days 1 hour ago) and read 7579 times:

A Flight Level (FL) is an altitude above a pressure this pressure is always = 1013 HPa. (we call that the Altitude-pressure)
FL370 is 37,000ft over 1013 HPa.

You have to know that pressure is always changing so we use 1013 to be at the same altitude-pressure than other planes...

1 HPa = 30ft.

Imagine you are flying at 3000ft over 1000 HPa and another aircraft is flying in your direction at 3600ft over 1020 HPa. Acctualy you are both flying at the same altitude! both of you are on the isobare 900 HPa. 3000ft + 13 HPa (390ft) = 3390ft and 3600 - 7 HPa (210ft) = 3390ft!
both are flying at 3390ft over 1013 HPa.

But in reality we cannot fly at 3390ft over 1013 HPa... we have to fly some specific FL like 5000ft (FL50), 5500ft (FL55), 6000ft (FL60), 6500ft (FL65)...or 37,000ft (FL370)...that's because we need to have secure altitude separations between aircrafts. (that's the semi-circular rules but I'm not going to explain that it will be too much for the moment).

That can be very confusing when you make a long trip! So the rule say that we have to fly an altitude-pressure (over 1013 HPa) when we are above a certain altitude (in my country when you pass 4500ft climbing over the sea presure [what change all the time] you need to set 1013 HPa on you altimeter...). It's more secure!

I know it can be a bit difficult for people who doesn't fly...Anyway, I hope I'm understandable...
Hope it helps.
Julien from Belgium.
Regards  Smile


User currently offlineJoona From Finland, joined May 2001, 1038 posts, RR: 9
Reply 8, posted (13 years 4 months 5 days 1 hour ago) and read 7573 times:

Ok, there are different abbreviations used in here; I've seen HPa and Hpa...

But the correct is hPa  Smile

Joona  Smokin cool



1740 days idle. Beat that.
User currently offlineJulien.M From Belgium, joined Mar 2000, 143 posts, RR: 0
Reply 9, posted (13 years 4 months 5 days 1 hour ago) and read 7571 times:

yes that's right! hPa  Wink/being sarcastic

User currently offlineRhodan From , joined Dec 1969, posts, RR:
Reply 10, posted (13 years 4 months 5 days ago) and read 7571 times:

1hPa is 27 feet

User currently offlineTurbineBeaver From United States of America, joined Jan 2002, 1199 posts, RR: 0
Reply 11, posted (13 years 4 months 5 days ago) and read 7568 times:

Joona: my answers...

1) NO

2) YES

3) YES

4) NO

5) YES


am i right??????

TB


User currently offlineJoona From Finland, joined May 2001, 1038 posts, RR: 9
Reply 12, posted (13 years 4 months 4 days 11 hours ago) and read 7535 times:

Turbine:

1) Correct

2) Correct

3) Correct

4) Correct

5) Correct

Now it wasn't that hard was it?  Smile This is a pretty easy thing after you just understand frew facts:

- the meaning of Transition Level and Transition Altitude.

- Difference between Altitude (MSL/AGL) and Flight Level (FL)

And also one thing I forgot to mention is that below TL/TA you always fly according to local QNH / altimeter, and above fly according to QNH 1013 / altimeter 29.91 or 29.92, not sure which one it is.

Joona  Smokin cool



1740 days idle. Beat that.
User currently offlineILOVEA340 From United States of America, joined Oct 1999, 2100 posts, RR: 4
Reply 13, posted (13 years 4 months 4 days 11 hours ago) and read 7529 times:

370 is 37,000ft. 39 is 39,000ft and so on.

User currently offlineTimz From United States of America, joined Sep 1999, 6835 posts, RR: 6
Reply 14, posted (13 years 4 months 4 days 9 hours ago) and read 7526 times:

I believe SIA_B777 is still scratching his head. Let's try again.

An altimeter is a pressure gauge, right? Somehow, someone has decided that the pressure at 37000 ft altitude is X pounds per square foot, or Y Pascals, or whatever. So they manufacture the altimeter so it reads 37000 ft when the outside pressure is X lb per sq ft. But of course the actual pressure at 37000 ft varies from day to day and from place to place. So if we want to fly at a constant 37000-ft altitude, how do we do it?

The answer is, we don't try to. Instead we just fly along at whatever altitude happens to have a pressure of X lb per sq ft. We call this altitude Flight Level 370. Our actual altitude might be a thousand feet (?) higher or lower than 37000 ft, but as long as all the aircraft up there are following the same rules we'll be okay.

Take a look at http://www.digitaldutch.com/atmoscalc/index.htm

If you key 37000 ft into the input box it will tell you that the "standard" pressure at 37000 ft altitude is 452.438 pounds per square foot, or 21662.7318 Pascals. Those are the "standard day" values of X and Y. So the answer to your question is actually pretty simple: FL370 is the altitude where the actual air pressure, at the moment, is 452.438 lb per sq ft.

For the formulas used to define the "standard day" see http://www.best.com/~williams/avform.htm#Altimetry


User currently offlineSdate747 From United States of America, joined Oct 2000, 272 posts, RR: 0
Reply 15, posted (13 years 4 months 4 days 8 hours ago) and read 7514 times:

What is "HEAVY"? I hear it a lot on ATC and I don't know what it is.

Thanks
Sdate747


User currently offlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4200 posts, RR: 37
Reply 16, posted (13 years 4 months 4 days 8 hours ago) and read 7517 times:

An aircraft has "heavy" attatched to its call sign if its Maximum Gross Takeoff weight is over 255,000 pounds. It may or may not be over this weight, it is its maximum certified weight that determines the callsign.


Chicks dig winglets.
User currently offlineSIA_B777 From United States of America, joined Apr 2001, 469 posts, RR: 1
Reply 17, posted (13 years 4 months 4 days 7 hours ago) and read 7492 times:

wow

i am a bit confused, however my understanding for FL370 is pretty clear, it is the hPa stuff that makes me go  Confused  Nuts


User currently offlineJoona From Finland, joined May 2001, 1038 posts, RR: 9
Reply 18, posted (13 years 4 months 4 days ago) and read 7485 times:

SIA_B777, also remember that above Transition Altitude the altimeter / QNH is always set to STANDARD, in this case 1013 hPa or 29.91

Joona  Smokin cool



1740 days idle. Beat that.
User currently offlineFXRA From United States of America, joined Jul 1999, 706 posts, RR: 2
Reply 19, posted (13 years 4 months 3 days 22 hours ago) and read 7469 times:

STandard pressure is used about a certain height, in the US 18,000 or FL180. At that height, the altimeters are adjusted to a pressure of 29.92. This is the same for all aircraft. SInce the pressure at that atltiude still varies, your may not actually be exactly 18,000 ft above MSL. but since everyone esle is on teh same page it works out.

Below FL180, you must get pressure ratings from WX stations enroute and constantly adjust as needed, or you risk flying into the groud. Especially after bpassing from hi to low pressure areas.

I think i got that right... i hope so, i get to go through the same line of questioning and more tomorrrow with the FAA...

later



Visualize Whirled Peas
User currently offlineBuff From Australia, joined Mar 2007, 0 posts, RR: 1
Reply 20, posted (13 years 4 months 3 days 21 hours ago) and read 7467 times:

The technical standard pressure in millibars is 1013.25 rounded up to the nearest 1/100th mb. An hectopascal is roughly 1/10 of a millibar.

The correct international setting is in fact 1013.25 but on drum style pressure altimeters is accepted at 1013 because the rest is a guess. Airbus uses a push/pull knob simply giving the phrase "STD" for use in the FL's.

"Pressure Altitude" - FL370 or any other FL can be considered more a constant pressure level rather than an actual altitude. Atmospheric pressure in the lower levels (<18,000') has an average decrease of about 1" of mercury in the mercury barometer. Above 18,000, the rate of decrease in pressure is less. Until recently, as aneroid instruments (common altimeter) had variable accuracies in the higher levels, FL spacing in the HL airspace was 2,000'.

With many modern aircraft now flying the NAT's, the Pacific and soon to be continental Europe and North America, most utilizing highly accurate Digital Air Data Computers, vertical spacing is being reduced to 1,000' under a program entitled Reduced Vertical Separtation Minima or RVSM.

Aircraft must meet minimum technical standards in order to participate in RVSM airspace. If they don't, then they are not allowed to fly into it. RVSM was first introduced into the North Atlantic in April of 1997, then in the Pacific in 1999 (I believe). It will be in use over continental North America in early 2002.

Active FL's for RVSM over the Atlantic are from FL285 to FL420 inclusive. Aircraft not certified to fly in RVSM airspace must enter RVSM airspace either underneath or overtop of the limiting FL's. Once continental bodies start participating in the program, flying overtop will be moot as one would have to fly through it to get on top.

Hope that adds something,

Best Regards,

Buff


User currently offlineTimz From United States of America, joined Sep 1999, 6835 posts, RR: 6
Reply 21, posted (13 years 4 months 3 days 20 hours ago) and read 7455 times:

Other people are saying a millibar is the same as a hectoPascal. So is it 1/10 after all?

User currently offlineJan Mogren From Sweden, joined Dec 2000, 2043 posts, RR: 50
Reply 22, posted (13 years 4 months 3 days 20 hours ago) and read 7445 times:

millibar=hPa
just a new name
/JM



AeroPresentation - Airline DVD's filmed in High Definition
User currently offlineBuff From Australia, joined Mar 2007, 0 posts, RR: 1
Reply 23, posted (13 years 4 months 3 days 18 hours ago) and read 7429 times:

Dang metric system! Got them confused. Local weather on the weather channel is in kPa which is to what I mistakenly referred.

Buff was wrong!

Grievous apologies.

Oh well, it'll probably happen again...


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