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Autorouter issues and questions (merged)

I rather meant that the wind forecast is too imprecise.

A couple of weeks ago, flying in Greece, it was 20-30kt off.

Administrator
Shoreham EGKA, United Kingdom

The issue is, it’s just a forecast. In flight winds will never always be 100% accurate.

When I flew to Newquay it was 30 minutes out, and only 10 minutes out on the return. Flew to Doncaster/Liverpool and very accurate, except for 10 minutes from the STAR to the landing. Which is why I questioned what flight times it is giving. Is it from departure to landing without the SID/STAR data (Which means more mileage and more fuel burn). It would explain why it’s well out.

Peter wrote:

I rather meant that the wind forecast is too imprecise.

A couple of weeks ago, flying in Greece, it was 20-30kt off.

Qualified PPL with IR SP/SE PBN
EGSG, United Kingdom

It probably can be accurate for a jet or a TP, but the way one flies piston aircraft is this

  • if wx is nice, climb to ~FL100, lean for peak EGT (or LOP) and sit there
  • if there is IMC, climb to VMC on top, and lean for peak EGT (or LOP) and sit there
  • continue the flight by reference to the fuel totaliser (nothing else really matters, other than the destination airport closing time)

So on any given day there is a lot of variation in the fuel burn, the TAS, and due to winds the GS. If you get an accurate result, you are either flying in nice wx and setting the speed to match what you entered into the flight plan, or it is luck

Administrator
Shoreham EGKA, United Kingdom

I guess you don’t have an issue with payload though? So you usually fill to the bottom of the top of the tank? I only have a useful load of 321kg and a full tank is 124.62kg. Giving only 2 Pax and bags. Although full fuel gives me 1100NM at 50% power.

Anyway I’ve done almost 5 years flying in this DA40 and never ever landed with less than 90 minutes fuel on all flights. I just like to accurately know what my fuel burn will be. If our flight time is longer than what I anticipate, I’ll just divert well before hand.

Peter wrote:

It probably can be accurate for a jet or a TP, but the way one flies piston aircraft is this

if wx is nice, climb to ~FL100, lean for peak EGT (or LOP) and sit there
if there is IMC, climb to VMC on top, and lean for peak EGT (or LOP) and sit there
continue the flight by reference to the fuel totaliser (nothing else really matters, other than the destination airport closing time)
So on any given day there is a lot of variation in the fuel burn, the TAS, and due to winds the GS. If you get an accurate result, you are either flying in nice wx and setting the speed to match what you entered into the flight plan, or it is luck

Qualified PPL with IR SP/SE PBN
EGSG, United Kingdom

pilotrobbie wrote:

When I flew to Newquay it was 30 minutes out, and only 10 minutes out on the return. Flew to Doncaster/Liverpool and very accurate, except for 10 minutes from the STAR to the landing. Which is why I questioned what flight times it is giving. Is it from departure to landing without the SID/STAR data (Which means more mileage and more fuel burn). It would explain why it’s well out.

Yes your IFR arrival time is wtr to some navigational fix overhead not your landing time, in the case of STAR the fix will be the IAF, without STAR the fix is overhead runway ARP

Remember IAP is not part of an IFR flight plan only SID+Airway/Route+STAR are included, first reason being the arrival runway is unknown and may change, you could go-fly opposite runway IAP or circle to land and AutoRouter has no way to guess you could fly a visual approach to Newquay: cowboy direct under IFR using your eyes at 190kts before 2nm short finale rather than circling like a turtle while following their 15nm procedural DME arc to Newquay

Last Edited by Ibra at 05 Oct 14:37
Paris/Essex, France/UK, United Kingdom

I seem to remember learning that IFR the ETA at destination is always the IAF whereas in VFR it is vertical the airfield. Has this changed?

France

Peter wrote:

I use the wind forecast. However the wind calculation, and the aircraft perf model, are so imprecise it does not make sense to ask whether the STAR is included

That’s interesting. My experience is that the wind forecasts are so precise that enroute flight times are typically accurate within 1-2% – and then I usually fly aircraft that are 30-40 knots slower than yours. But of course we fly in quite different parts of Europe. The precision of the wind forecast may vary with the location?

If you get an accurate result, you are either … and setting the speed to match what you entered into the flight plan…

Well, of course I use the same power setting in my flight planning that I intend to use in flight. Why should I not?

Last Edited by Airborne_Again at 05 Oct 16:17
ESKC (Uppsala/Sundbro), Sweden

I use the same power setting in my flight planning that I intend to use in flight. Why should I not?

Because the only way to fly at altitude, say FL080+, is wide open throttle and peak EGT or LOP.

It would be quite daft to partially close the throttle when above say FL080, and one can’t open it anymore than wide-open.

But of course we fly in quite different parts of Europe. The precision of the wind forecast may vary with the location?

Maybe, but I suspect you a) fly low down so can adjust the TAS to match the AR numbers (which takes out one of the variables) and/or b) got lucky. For sure, the general picture from windy.com (ECMWF; I never use GFS anymore) is broadly speaking usually in the right ballpark, but “broadly speaking” can be 10-20kt off.

Administrator
Shoreham EGKA, United Kingdom

It would be quite daft to partially close the throttle when above say FL080,

That may be correct for a fuel injection system, but some carburettor engines benefit from a slightly improved intake manifold distribution from a slightly closed throttle.

Obviously if you planned to cruise at 55% which is a typical long range setting, a fuel injection or carburettor engine will not reduce to 55% full throttle until around FL100 plus. Carson speed, where 45% is a typical proxy, will not be full throttle until F130 plus.

Oxford (EGTK), United Kingdom

gallois wrote:

I seem to remember learning that IFR the ETA at destination is always the IAF

A bit of a side question, what if you are flying IFR to VFR airfield with no IAF like pilotrobbie does (doable in VMC, if the statement looks weird), for Stapleford EGSG, I guess that would be ETA to BPK VOR where London Control are likely to dump you? or it’s LAM overhead?

Last Edited by Ibra at 05 Oct 17:56
Paris/Essex, France/UK, United Kingdom
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