Hello guys~I have a question about the T/D, i found that in most cases for me, i can't follow the VNAV decend phase, because some STAR will need me to start decend far before the T/D which calculated by FMC, and i also instructed to decend by ATC at the same time, then i have to use V/S for my decend, so in real world, does the T/D only for reference? or it has other useful functions? Thanks!!Best RegardsTommy

Tommy,VNAV is usually used if able, but to satisfy the needs of ATC, it's often neccessary to use FL CH or manually edit LEGS page to suit the ALT and SPD restrictions. I've noticed, however, that PIC doesn't fly the descent phase restrictions too well. Climb restrictions are flown OK, but during the descent the a/c is busting the limits all the time. The T/D symbol indicates the point where a continuous IDLE descent should be initiated. It's a GOOD reference to plan the descents, but often it's just neccessary to do against the wishes of the FMC...Tero

If you have the STAR (including any speed/alt restrictions) properly programmed into the FMC, the T/D should be accurate for the STAR.Martin767 fetishistIt's a lot like life and that's what's appealing

Martin-There was a thread ages ago on the T/D vs ECON number. Not sure if PIC9767 FMC is set up the same way. Does the T/D include the intermediate points when calc TOD or does it just look at TOD/BOD points only?Tim_757

Hi,The FMC has a DES NOW function in the VNAV pages.This enables you to begin descent earlier than the ToD and the aircarft will begin a 500fpm descent until it establishes on the VNAV path later on.Mark

>The FMC has a DES NOW function in the VNAV pages. >This enables you to begin descent earlier than the ToD and >the aircarft will begin a 500fpm descent until it >establishes on the VNAV path later on. The DES NOW function begins a 1250 feet per minute descent schedule until intercepting the descent path. It also activates the FMC descent phase.Best Regards,

Ryan,thanks for updating the Descent Rate.Been a while since I have used DES NOW and assumed it began a minimum descent profile.Mark

My T/D point usually corresponds reasonably with the selected STAR. I'm not sure exactly how it works, but if you change any speed/alt restrictions in the descent, I think the T/D changes accordingly. But I don't fly PIC often enough to be completely certain about it. :-)Martin767 fetishistIt's a lot like life and that's what's appealing

Hey Tim,Wouldn't you say, the T/D function is a nice feature when flying into the Mega-hub at arnd 5am on a red-eye arrvl. But, during the majority of the day, ATC usually tries to tunnel the Arrivals underneath the outbound Depts, so most flts these days are usually starting down +50nm before the Optimum idle T/D pnt?Places like LGA come to mind, down in the weeds at FL180 some 100nm from the rwy.Marc

The DES NOW function begins a 1250 feet per minute descent Well I don't know if you are refering to the 757 here or not but Boeing says roughly a 1000FPM is encountered on the 767. I'm sure this varies a bit so we cannot say for certain a set descent rate. Tommy, To calculate the descent profile the FMC must know the end of descent point, the end of descent point is the lowest altitude constraint, for an ILS approach it's near the final approach fix &L;FAF&R; but before the glide slope intercept point. The end of descent point is entered automatically when you select an approach. To determine the descent path the FMC looks back from the end of descent point along the active route and calculates where the descent should begin. This is the top of descent point. The angle of the descent path is calculated to control speed for descent at idle thrust. Before reaching 10'000 feet the descent agle flattens to reduce airspeed to 240 knots. 240 knots is used as the command speed below 10'000 feet rather than 250 knots to provide a 10 knot buffer. Prior to the end of descent point the the descent path agian flattens so that airspeed at the final approach fix is at 170 knots. When you are within 200 NM from the top of descent point, the time and distance to the T/D are displayed on the cruize page. On the real bird well before you reach the T/D you would enter forcast winds for the descent path which would adjust the descent agle for any head or tail winds. This Also applies to using engine thermal anti-ice during the descent. If we could enter forcast winds etc for PIC the T/D would show a change. When the T/D point is reached, idle thrust and econ speed descent automatically initiates and the descent page becomes active and throttle hold mode engages. The airplane pitch will vari slightly to follow the FMC descent path which has been calculated to maintian econ speed. For most approaches the runway altitude constraint is shown in the upper left corner of the descent page. For ILS approaches the altitude is set to the G/S intercept altitude. One thing to remember, when approaching an airport where a speed restriction is not in effect, it may be removed by using the DEL key. Because the speed transition &L;240/10000&R; is automatically included when the FMC calculates the descent path, it should be removed prior to the T/D point. This also goes for entering any speed issued restrictions, when possible enter them prior to the T/D point. At times we will need to descend prior to reaching the T/D point. After activating the DES NOW function, The autothrottle will command a target EPR and the pitch mode changes to VNAV SPD. A shallow descent is flown until the calculated descent path is reached. Normally 1000FPM. When the calculated descent path is captured the autothrottle sets idle thrust and the pitch mode returns to VNAV PATH mode and maintains the descent path. If you must level off before reaching the E/D point, set the desired altitude on the MCP. When you reach the MCP altitude, VNAV disingages and the airplane levels off and the IAS window unblanks showing the existing speed. If you do not resume your descent in a very short time, it is usually not possible to recapture the FMC calculated descent path. We can then select another pitch mode such as FL CH to continue the desent. One last thing, if you encounter un forcast winds your airspeed will vary. If your airspeed loss is more than 15 knots when above 10'000 feet or 10 knots when below 10'000 feet, the autothrottle mode switches to SPD and thrust increases to FMC commanded speed. Likewise, if you encounter un forcast tail winds with an increase in airspeed 15 knots above 10'000 or 10 knots below 10'000 a DRAG REQUIRED message is displayed in the scratchpad. There is MUCH more but I hope this gives you a better understanding of how the FMC calculates the T/D point.Best Wishes, Randy J. Smith[h5]San Jose Ca[/h5][h3]" A little learning is a dangerous thing"[/h3]AMD XP 2100 |MUNCHKIN 512 DDR RAM |ECS[/b ][i] K7S5A MB[/i] |GF3 64 MEG |WIN XP PRO |MITSUBISHI DIAMOND PLUS 91 19"

Martin, This is only the case IF you make you changes BEFORE the T/D point.Best Wishes, Randy J. Smith[h5]San Jose Ca[/h5][h3]" A little learning is a dangerous thing"[/h3]AMD XP 2100 |MUNCHKIN 512 DDR RAM |ECS[/b ][i] K7S5A MB[/i] |GF3 64 MEG |WIN XP PRO |MITSUBISHI DIAMOND PLUS 91 19"

I find that FLCH works, but is not responsive enough for FS2K2 ATC. I've had many an IFR flight plan cancelled, because the aircraft took too long to settle into an idle descent at > 1500fpm, so unfortunately I now find I have to use V/S mode to keep it happy.

Tommy,If you have local knowledge or experience, go with that. However, the chart you depicted is an arrival chart. That is not intended to be used all the way to landing. There should also be an instrument approach procedure chart for your landing runway. That chart will have the appropriate IF and FAF altitudes (plus all the other relevant info).Kevin in CYOW

Thank you Kevin~I found the proper approach chart for rwy07L, IAF is 8000ft, FAF is 2000ft, really appreciate your help~ :-) Best Regards Tommy

Randy-Pretty good explaination, but you left out how the econ speed setting will "move" the TOD point closer or further away from the BOD-its kind of a nifty point when sorting it all out.The 757 is a very "slippery" aircraft and the "slowing at ten" takes up a good chunk of airspace (7 to 12 miles clean) which when the 757 was introduced caused a lot pilots to grab the speed brakes to slow the beastie down - not like the mild-mannered '27. The 767 sems to have that same quality. Tim_757