OnCourse Software

RALF9636 wrote:

Thank you Dave for your quick reply!

#1: It's clear that you don't descent without instruction by ATC. What I meant was: What is the common procedure: Does the pilot request ATC to get descent instructions when the TOD calculated by the FMC is getting close? Or is the pilot just waiting for ATC to initiate the descent?

#2: That clarifies it. It might also be the solution of the (non-)issue this topic is about. At least for me I guess it always was after being cleared via a STAR that I waited for a descent instruction. Which wasn't necessary as it was inlcuded in the STAR clearance!

Thanks again for this great software and support!

Ralf

Can't help further with #1 and we'll have to wait for someone who actually knows the answer

dmarch wrote:

RALF9636 wrote:

May I ask two questions in this context?

I also experienced PF3 occasionally not giving me descent instructions when I reached my calculated TOD (most of the time PF3 does give me descent instructions in time). It never was a big issue to me because I just requested 9000 ft lower once or twice and all was fine.

But here are my questions that arose in these occasions:

1. What is the standard real world procedure: Does ATC decide when the descent begins? Or is it the pilot who requests to initiate descent according to the calculations of the FMC?

2. When PF3 clears me via a STAR: Does that include a clearance to descend according to the published procedure? Or do I have to wait for a descent instruction?

Thank you very much!

Ralf

As far as I know, and I stand to be corrected as I'm no RW expert but...

#1 - It doesn't matter what your FMC states, you cannot change altitude without instruction from ATC

#2 - Yes, but ATC may still instruct you to descend to a different altitude at any time or re-route you or cancel the STAR altogether.

As Dave says #1 just because your FMC says it's time to descend you cannot, until ATC tell you to. however you can of course request a descent at that point if you haven't already been given instructions. Bear in mind that ATC do know your fpl so they will endeavour to get you down if they can when you want anyway. You are in contact with ATC already so they might say "Expect a late clearance." In which case you sit and wait!

#2 When your fpl finishes with a STAR your descent from cruise should idealy finish with the published FL of the STAR. That's the whole point of a published procedure. But ATC can clear you down to that FL or another as they see fit. For example arriving at Heathrow you would be descended to FL70 in stages according to traffic. Though they might still clear you to the runway from a higher level. It all depends on the amount of traffic. But if you loose radio contact then you must always fly the published procedure. So maintainig a listening watch is essential!

A discussion of RW pilots & controllers about descent clearances: http://www.pprune.org/atc-issues/15197- ... rance.html

CSA007 wrote:

A discussion of RW pilots & controllers about descent clearances: http://www.pprune.org/atc-issues/15197- ... rance.html

Very interesting, thanks for that link!

From the discussion there I conclude that in RW it is quite common that the pilot asks ATC for descent when closing in to the calculated TOD.

So this might be something that could be implemented in PF3 for even more realism. Quite tricky regarding the phraseology though since even the real world professionals are discussing how to put it.

BTW: Is the instruction "descend to ... at pilot's discretion" PF3 sometimes gives, equivalent to the "when ready descent ..." instruction mentioned in that discussion?

Regards

Ralf

RALF9636 wrote:

CSA007 wrote:

A discussion of RW pilots & controllers about descent clearances: http://www.pprune.org/atc-issues/15197- ... rance.html

BTW: Is the instruction "descend to ... at pilot's discretion" PF3 sometimes gives, equivalent to the "when ready descent ..." instruction mentioned in that discussion?

Regards

Ralf

If you have some distance between waypoints where the first is the last one at cruise level and the next requires you to have descended then PF3's "descend to ... at pilot's discretion" is quite useful. For example flying into Hong Kong there is an altitude constraint at CHALI of FL160 but at RAGSO I am at FL240 i.e. cruise level. There is about 100nm between the two waypoints so I elect to initiate my descent immediately at no more than 1,000fpm. Sometimes PF3 will give me "At your discretion" and sometimes not. With the discretion option I could continue at cruise level and then make a faster descent later. However If asked straight to descend I still would not descend to FL160 and then fly 80nm at a lower altitude (in this case). In real life ATC if they wanted me to descend all the way quickly they would say "Expedite your descent to ..". As Captain you have to make the decision as to how quickly you need to descend depending on the distances involved. PF3 I think gives the right mix of instructions and works well if you have given it a well planned fpl.

Just curious…why should the distance between waypoints have anything to do with the descent clearance? To take an extreme example, supposing there was 500 miles between the waypoint with the vertical constraint and the previous one, would PF3 give a descent instruction 500 miles before the the constrained waypoint?

Andy

vololiberista wrote:

Sometimes PF3 will give me "At your discretion" and sometimes not. With the discretion option I could continue at cruise level and then make a faster descent later.

Thank you for that clarification.

awralls wrote:

Just curious…why should the distance between waypoints have anything to do with the descent clearance? To take an extreme example, supposing there was 500 miles between the waypoint with the vertical constraint and the previous one, would PF3 give a descent instruction 500 miles before the the constrained waypoint?

Andy

Having never had a fpl with that kind of distance between the last cruise wypt and the start of a STAR I haven't been able to test it in PF3. No the distance itself in real life has no bearing. It's how far you are from the target and what kind of airspace you are in and how busy it is that influences real ATC.

Andy[/quote]

Having never had a fpl with that kind of distance between the last cruise wypt and the start of a STAR I haven't been able to test it in PF3. No the distance itself in real life has no bearing. It's how far you are from the target and what kind of airspace you are in and how busy it is that influences real ATC.[/quote]

Sorry, my question was imprecise; forgive me. I was referring to PF3. If that scenario existed in PF3, what would be the result. My point, clumsily stated, was that PF3 should be calculating descent points independent of waypoints and irrespective of whether there are approach procedures in play.

I know how it works in real life...I've been there

Andy

I also had a descent profile issue on my last flight.
PF3 correctly initiated my descent but then kept me at FL260 until my last waypoint which was only 30 nm from my destination. I had set an altitude of 5000 ft on the Adjust .. Flight Plan page.

I had used accelerated sim rate on that flight before but since the initial descend instruction was correct I don't think that had an influence.

Regards

Ralf