It's easy to see how to set TA for departure area; however I don't see a place to set the FMC TA for the destination (as with the MD11).

Is it even possible to do this with the T7 FMC?  Is this even necessary? 

Thanks,

   Ken Boardman

Are you looking for VNAV FMC button -> Next Page (until you hit DES), and then SPD TRANS?

go to FMC -> VNAV button -> Forecast -> and then you can change the T.A.

Sidenote: when climbing, it's transition altitude (feet -> flight levels), and when descending (which is what you were asking for), it's transition level (flight levels -> feet). This procedure described above for setting the TL also applies for the 747.

Many thanks for the very informative replies.

Best to all,

Ken

Sidenote: when climbing, it's transition altitude (feet -> flight levels), and when descending (which is what you were asking for), it's transition level (flight levels -> feet). This procedure described above for setting the TL also applies for the 747.

 

You can also set the Transition Altitude just below Transition Level on the same "Forecast" page.  I was a bit surprised by this section, as TL is very variable, and depends upon the atmospheric pressure, while the TA is constant.  Also, when descending the TA is more important, since at or below that altitude the altimeter is set to local pressure.  You would never be cleared to an altitude between the TL and the TA, as you could  come dangerously close to an aircraft at the transition altitude.

 

Mike

 

Edit: I'm wrong about being able to set the TA on that page -- only the TL.  In the example in Tutorial #1 the TL is fixed at OMDB at FL150, TA is 13000, but at the departure airport, VRMM (Maldives) the TL is set by ATC (i.e. it is variable), while the TA is fixed at 11000.  TL is also set by ATC at Heathrow and many other airports.  Seems to me the more important altitude is the TA - at or below go to local altimeter.

It's easy to see how to set TA for departure area; however I don't see a place to set the FMC TA for the destination (as with the MD11).

Is it even possible to do this with the T7 FMC?  Is this even necessary? 

Thanks,

   Ken Boardman

 

I have to look at this to keep it straight in my head:

 

http://www.skybrary.aero/index.php/Transition_Altitude/Level

 

as far as the FMC it doesn't automatically change your altimeter so I think it's really only part of the fuel forecast? On this new T7 I 'm forced to rethink things because I never did transcontinental flights so now you have to keep this in mind as well as transition levels. Gets confusing and I think the rules are diff in Europe compared to the US as far as when to set this?  I understand the concept but when to change settings and where and how these values in the FMC impacts it is confusing.

 

Edit: Also when to change based on company SOP has me baffled as well I just don't understand how the pilots and ATC can assure clearances in a busy area when everyone is operating with different settings.

as far as the FMC it doesn't automatically change your altimeter so I think it's really only part of the fuel forecast?

 

Just did a little experimenting and found that the CDU setting for TL does affect the altimeter setting in that when descending, the "STD" display on the PFD switches from green to amber as a warning, about 400ft below the TL.

 

As the very good article you cite points out, the TL usually varies according to pressure, while the TA is fixed.  What bothers me is that sometimes the TL is unknown, but it is crucial to know when you are at or below the TA so that your altimeter is showing the same accurate altimeter readings as everyone else, as well as knowing your altitude accurately.  My "temptation" would be to enter the TA instead of the TL in the TL box on the CDU during a descent and approach.  Seems to me the only reason you really need the TL is to make sure ATC doesn't err by assigning you an altitude in the "no man's land" between TL and TA.

 

I never was aware of this until I started flying outside the US and paid attention to the charts.  It can be very important when the TA is only 6 or 7000 feet, because there can be many aircraft not too far apart in altitude in fairly close proximity.  But as long as you 1) set the altimeter to local pressure at and below TA, and 2) don't level off between the TL and the TA, you should be fine.

 

Mike

If you are cleared to a Flight Level by ATC, that's on Standard Altimeter/QNH (QNE?)

 

If you are cleared to an Altitude... ie something that doesn't have the words "Flight Level" in it, then you'll be wanting the local barometric altimeter setting, be it in, mm, hpa, QNH, QFE or whatever the ATC is using in that part of the world.

 

Look at charts to find the transition altitude and FL. Sometimes the transition Level or Altitude will be "By ATC". which basically means... when you hear the absence of "Flight Level" in your decent instruction, you want to be off altimeter setting "STD".

 

Charts might give you a hint as to where this might be. In which case, set it up early so the STD or altimeter setting isn't all yellow on the PFD for long.

To clear up two points of confusion:

 

When descending the FMC uses the TL to 1) improve the descent path calculations and 2) warn you when to change the altimeter setting by turning the indication amber.

 

TA is when you change over from local to standard going up, TL is when you change from standard to local going down*. In the US TA and TL are 18,000' and FL180 respectively, outside it's often set by ATC depending on local pressure. Usually the TL will be within 1000' of TA. ATC will not assign you an altitude between TA and TL.

 

*Setting your altimeter to local as soon as ATC clears you to an altitude below TL is also OK to the best of my knowledge.

 

Unless on IVAO/Vatsim the assumption TA = TL works fine. On Vatsim TL is often broadcast in the ATIS.