Cannot capture a selected altitude

[Adrian West 6]

Hi again.

I am having further problems with the departure. I am setting the first cleared altitude, but the autopilot ignores this and flies right through it. From previous experience of the G1000 on different aircraft I believe that setting an altitude should arm ALTS. However I am seeing ALTS disappear as I climb out, and I cannot find any way of resetting it. My initial climb is being done through VS mode. I do not engage FLC until I am climbing to a higher altitude and have the speed stabilised around 225 KIAS. Please could somebody advise. Thanks.

Adrian

[Adrian West 6]

As an update to my earlier post, I have now tried 2 scenarios:

1. Set initial cleared altitude and vertical speed before take off. The aircraft holds the vertical speed correctly, but ignores the white ALTS and flies straight through it. 

2. Set vertical speed only before take off, and then set cleared altitude immediately after take off. This then erased the vertical speed, and I had to set both vertical speed and altitude again. 

Surely option 1 ought to be possible, and should be the correct procedure? I have used this option for several years on a King Air with a G1000, and it works without a hitch. So what is wrong with the Phenom AP? If there are bugs (which I have read there are), what is the best workaround? Thanks. 

Adrian

[kenny584 77]

Hello Adrian.

I am sorry to read of your problems and know how frustrating this aircraft can appear to be. A lot of people's problems come from not managing their airspeed. There is no autothrottle in the 300. This means that the pilot has to monitor the indicated airspeed and match it to their selected airspeed. It appears that some folks are flying it like an airliner and expecting too much of or not fully understanding the FADEC system.

Anyway, Here is what I see and do when changing altitude or flight levels. Initially, on departure, if your SID has a stop altitude of 6000 feet then set that in the Altitude ribbon as normal. Then decide on what seems a sensible VS, say for an example, 2000 feet. I know the aircraft will climb steeper than that but this is just an example. Then select a sensible airspeed, say 220. Set this in the Selected Airspeed box above the speed tape. On departure you should be seeing VS2000FPM (in Green) and ALTS (in White) in the Flight Mode Annunciator (FMA) in the PFD. I am carefull to select CON\CLB for the thrust levers and match the indicated airspeed to that selected. On approaching 6000 feet, both the VS2000FPM and ALTS go off and PIT (in Green) will appear in the FMA. The VS will reduce quite quickly and as you reach 6000 feet PIT goes off and is replaced by ALT (in Green) in the FMA. Be careful then to adjust the thrust to maintain selected airspeed.

Let's now say you anticipate a climb to 41000 feet, FL410. Select a sensible airspeed, this will determine your rate of climb. Let's say 250 knts as an example. select 41000 in the Selected Altitude box and adjust the indicated airspeed to match the selected. Then select FLC mode. FLC (in Green) and ALTS (in White) will show in the FMA and the aircraft will pitch up at a VS to maintain 250 knts. You will have to monitor the indicated airspeed and adjust the thrust to match the Selected Airspeed otherwise as the aircraft climbs into thinner air it will start to pitch up and down in an attempt to maintain 250 knts. This is the FADEC system managing the engines. The airspeed may start to fall off as you climb and you then have to decide if you wish to maintain airspeed or VS. Adjust either one to maintain the other if that makes sense.

There is a great pdf by Embraer here...http://aircraftstudyapps.com/wp-content/uploads/2019/04/Phenom-300-compressed.pdf

Section three covers the Automatic Flight controls. I hope I have not come across as teaching you to suck eggs and perhaps your system is behaving differently from mine but I can honestly say that once you get a grip of the systems this is a beautiful aircraft to fly. I know a lot of people moan about it and say they have problems but I think it all comes down to understanding the routines.

Best Regards...Ken.

[FDEdev 955]

5 hours ago, kenny584 said:

1. Let's now say you anticipate a climb to 41000 feet, FL410. Select a sensible airspeed, this will determine your rate of climb. Let's say 250 knts as an example.

2.You will have to monitor the indicated airspeed and adjust the thrust to match the Selected Airspeed otherwise as the aircraft climbs into thinner air it will start to pitch up and down in an attempt to maintain 250 knts. This is the FADEC system managing the engines.

3.The airspeed may start to fall off as you climb and you then have to decide if you wish to maintain airspeed or VS. Adjust either one to maintain the other if that makes sense.

Thank you for taking your time for this extensive explanation. 🙂  A few notes nevertheless

1. The correct climb speed is 225kts/M0.60. The crossover altitude where you should switch from kts to mach is ~FL295. 

2. The pitch oscillations usually only occur due to changes in wind speed/direction and turbulence. It's the same IRL and the reason why pitch modes which are based on speed can be rather uncomfortable. This has nothing to do with FADEC. The only thing FADEC basically does is to keep the engine within its limits.

You should always climb at max climb thrust and adjust pitch or VS to keep IAS within e.g. + 5kts. That way you avoid the pitch oscillations if the air isn't totally smooth. 🙂

In totally smooth air FLC should work nicely.

3. Since the climb speed above FL295 is Mach, IAS starts to continuously reduce below 225kts once you are above FL295. You maintain Mach not indicated airspeed.

One more note:

If you have to do an intermediate level off at e.g. FL300 and you are cleared to FL410 you trade kinetic energy for potential energy.

Since you already going much faster than M0.6, you select a higher VS than your aircraft is capable to maintain when you start climbing at max climb thrust.  As the Mach number decreases from e.g. M0.76 towards the optimum M0.60, you either reduce the VS so that the Mach numbers stays at 0.6, or enable FLC to maintain M0.60.

Not sure but AFAIR there's a bug in the Carenado version and if you switch to Mach, the Mach number starts reducing, which it definitely shouldn't do!

 

 

 

Edited April 9, 2020 by FDEdev

[Adrian West 6]

Hi both!

Thanks for your replies last week. Sorry for the lateness in replying - Easter came in the middle and I've also spent quite a lot of time watching FSMania's very helpful videos of his flights from Brazil to Wichita. I've so far watched the first 2 legs only and that has already armed me with a lot of information, including setting your initial climb speed on take off to something lower like 160 kts and then steadily increasing it by small amounts until you reach the optimum 225 kts. That way you are in better control of the aircraft and it stops the "porpoising" that FLC can otherwise create. I have just successfully completed a flight from EGKK to EGPH mainly using FLC on the climb to cruise and VNAV on the descent. 

The EGKK SID requires an initial hold at 5000 ft for some considerable distance to avoid traffic into or out of EGLL. It then steps up to 6000 ft, which I managed with VS, and then at the end of the SID I could then go back into FLC up to my cruising altitude of FL350. It just requires keeping your beady eyes on the airspeed and adjusting the power accordingly.

It is a lovely aircraft to fly!

Adrian

[n116dh 4]

Gentlemen,

I too am now experiencing loss of ALTS, going to PIT and flying right by selected altitude no matter, it seems, whatever I do for vertical nav while sequencing through take off.  My problem seems to have started when I reinstalled to v2.1 while working with Carenado (trying to get the aural sounds to work).

So, Mr. Adrian, if you please, did your loss of ALTS and flying passed selected altitude go away when you followed the sequence you describe?  And would you mind providing your Carenado version?

Thanks a lot.

[Adrian West 6]

Hi. 

I'm not quite sure what you mean by the "sequence". Basically I watched the Fsmania videos and studied how he handled the take off and climb. My departures are now stable 90% of the time. However there is something not right with the default autopilot on this aircraft, particularly with altitude hold. A week ago I was descending into an airport on VNAV, and the autopilot ignored the requested altitude. I tried turning off VNAV and selecting ALTS, but this didn't work either. I was forced to turn off the autopilot and fly the approach manually. 

I would highly recommend watching the Fsmania videos on YouTube. They are very informative. By the way, I don't have the version number to hand, but I have the latest version of the aircraft. 

Adrian