All Of A Sudden IAS,Alt Loss

Set out on a flight, route and fuel loading created by SimBrief, from FSDT's KJFK v2(New York) headed for KUNV,(State College) a mere 168 miles away. Reached CL at 22000ft all running perfectly normal, when all of a sudden, at exactly same point, waypoint ETX(East Texas) as happened last night, the aircraft from Cruise Power speed and at 22000ft started losing IAS and ALT, and became awkward to even fly by hand as it started to veer left, right and go bananas. Had to abort the sim.

Any clues as to why this would happen, and yet I have used it in Europe, e.g. LOWI-EGCC with no problems at all?

Comments

  • Hello, a first request, have you been traveling with a weather program and have you activated the same weather both times?
    If there were suddenly strong gusts of wind, the autopilot remained active, if so, with which modes?

  • edited June 2020
    Your issue sounds more related to an icing induced event on either airframe or engines if the proper icing systems were not activated. Difficult to say as no one knows what conditions you were flying in.

    Cheers
  • Thanks for that reply.

    But it was only a daylight flight, no weather engine employed, just the default P3Dv4.5 weather, and I just tried the very same route in a PMDG 737,same ALT, and not a glitch. Perfect flight. But Ill re-try and this time switch on the AI

  • Depending on which weather theme is invoked within the sim icing may still occur unless your were flying with fair weather or something clear of precipitation

    I would try the route again and see if the issue can be repeated..
  • Thanks again. No defined weather, just the sim's fair weather. Am re-flying the same route again with AI switched on this time, same fair weather engaged. So, let's see if the same yo-yoing happens again. Will report back.

  • Update as promised. It seems leaving the anti-ice switches was what caused that erratic behaviour, because as soon as I switched it on in prepping the aircraft, the very same route, except dusk this time, as compared to this morning's clear daylight, I had a problem-free flight. Now, I have no idea as it was New York to State College whether I was over the Appalachian Range that may have caused ice detection, I have not a clue, as I was using nil weather engine, and default sim fair weather.

    Anyways, now I know what led to that odd behaviour yesterday and this morning.

  • Well if there was no icing the condition should not caused any issues with loss of airspeed, altitude or any other associated performance issues.

    Trying the previous scenario to see if you can replicate the issue would be interesting.
  • Thanks again for your reply. Will give it a try as soon as daytime free time allows, and report back

  • Thanks again for your reply. Will give it a try as soon as daytime free time allows, and report back

  • Okay, can now confirm, same routing, same altitude, did not switch the AI on, at same place along the route, after reaching 22000 ft with no problems at all, until this showed up and it reverted to what I first reported.

  • Default sim fair weather was loaded

  • Would have been nice to see the ED or overhead and glare shield / pedestal. When I see these messages, I wonder if the engines are still running? The messages "Tank Fuel Low" and "ENG Fuel Press" suggest that you run out of fuel or that it does not come to the engines. Very strange.

  • There has to more to this puzzle that you are not aware of or not enlightening us about.

    1. Maybe a route of flight flown
    2. Planned Fuel Load (if any). Possible improper fuel loading
  • Thanks for the 2 replies.

    1. Will upload the SimBrief-created flighplan
    2. Fuel was also calculated by SimBrief but as it was a very short journey of 185 including SIDs and STARs, I had via the MCDU loaded 4000kgs,and via GSX refuelling around 7500 lbs, so,fuel wise, I seemed okay. Pax was 74, cargo 10
  • When climbing this morning

  • MCDU Payload

  • The route map

  • This is round about where things started going haywire

  • And there you have all the information I hope you wanted

  • You also have to refuel, if I see the right one you have around 270 kg on board

  • Copy thank you for the information, however I have to ask?

    The fuel page that you show in the FMS is what you were planning to put on the aircraft, correct? However looking at your fuel gauges you are practically flying on fumes as you only have 265 kg of fuel. So I am suspecting that if you are loading the aircraft via the cpan your fuel loads are not planned correctly.

    There are 2 boxes for fuel in the cpan... The top one is for preffered fuel and the bottom one is your intended fuel burn for the trip.
  • Funny, you mentioned that because that was a screenshot I took while climbing out of New York this morning. And I did tell GSX to load 7000lbs of fuel, which I thought for a short hop was adequate enough. Either GSX screwed up, or I did not check the cpan.

    Now I that am aware, thanks to you two, what caused that weird AP repeatedly switching off and the IAS bleeding speed, I will make another attempt, no AI switches on, again, and this time monitor the fuel without GSX

  • A/Ice is only required of your temps are below +10 and there is visible moisture and of if the ice sensors indicate ice acretion
  • Thanks for that. While I am at it, where can I get a real good YouTube or text Tutorial on the programming of the VNAV?

  • In the forum here you can actually find everything, which is not that difficult. You inform yourself in the cruise about the first height restriction, which can be found on the STAR or at the latest at the IAF / IF. This determines the start of the descent on the T / D. On the VNAV site you look for this point, because all restrictions are noted here at the waypoints. You then select the sink rate (usually 1800 ft) and confirm this. The T / D is now shown to you. The VNAV Deviation Bars appear 2 minutes before reaching the T / D, you will receive the corresponding information on the PFD. You can now turn in the first target height on the MCP and arm VNAV. The descent then starts automatically at the T / D. This is also clearly described in the manual.

  • An example

    Find the first height restriction on STAR or IF in the charts and / or on the LEGS Page. In this example it is OBANO it FL11000 or above.

    Call up the VNAV page on the CDU and look for the suitable waypoint that you need for VNAV programming, i.e. OBANO, the 3rd

    Enter 3 in the highlighted field and press ENTER

    OBANO now appears with its restriction and the next field is highlighted, but we can generally not need to be skipped with ENTER.

    The specified height restriction is now highlighted and can be confirmed with ENTER. If you would like to use a waypoint without a specified restriction, then enter the desired value here and confirm with ENTER.

    Now the sink rate is Now the sink rate is highlighted, the default is -1800, but can be changed, confirm again with ENTER., the default is -1800, but can be changed, confirm again with ENTER.

    The system now has all the necessary information and calculates the T / D with distance and arrival time

    The deviation bars appear 2 minutes before the T / D is reached

    We now turn the desired target height, so here FL11000 + ALT SEL and armed VNAV in the MCP

    As we get closer to the T / D and nearing the VNAV PATH, the deviation shelf begins to move

    When the VNAV Path is captured, the AP modes change from ALT Sel to VNAV PATH.
    In the course of the descent, we then have to set the height in the MCP to the new target heights and do not forget to press ALT SEL in order not to accidentally sink too low.

  • @FraPre said:
    In the forum here you can actually find everything, which is not that difficult. You inform yourself in the cruise about the first height restriction, which can be found on the STAR or at the latest at the IAF / IF. This determines the start of the descent on the T / D. On the VNAV site you look for this point, because all restrictions are noted here at the waypoints. You then select the sink rate (usually 1800 ft) and confirm this. The T / D is now shown to you. The VNAV Deviation Bars appear 2 minutes before reaching the T / D, you will receive the corresponding information on the PFD. You can now turn in the first target height on the MCP and arm VNAV. The descent then starts automatically at the T / D. This is also clearly described in the manual.

    Done all that but it never comes up in the PFD as flashing VNAV for me to trigger the VNAV button. Nevertheless, thanks, will try and follow your instructions.

  • @FraPre Tried the above as you suggested, even saved those screenshotsof yours of of the MCDU to refer to for a flight from KMCI to KIAD, and did exactly as per your instructions above, put the first descent ALT, but that deviation bar did not show any V at the top. See attached.

    Where am I going wrong, please?



  • If you have adopted the 1800 with ENTER on the VNAV page, only then will it be calculated where the TOD is and this is also displayed on the VNAV page. The TOD should be a bit ahead of MGW, since you have to mine 17000 ft.
    VNAV programming must of course also be done in good time. If the time at cruising altitude is only short, you should program this immediately after reaching the cruising altitude, not that you have already passed the TOD long ago.

    However, some things on your PFD also do not fit (Speed, 15000 ALT blue), but only by the way.

  • I did set a height restriction of 15000 from 25000 cruise ALT as I could see nothing in the FPL and had no charts to refer to, long before I got to MGW, and anticipated that 2 minutes warning to be ready to trigger the new ALT, but it came and went and still nothing in the deviation.

    It was an 891 miles flightplan, so there was enough time spent at Cruise, and I programmed the VNAV following your screenshots of the MCDU exactly.

    Should not the ALT SEL show up in blue, then?

    Going to give it another go, later.

  • edited July 2020

    If you have "programmed" everything correctly, the calculation of the TOD should appear on the VNAV page at the end (circled in blue). I can only see the previous picture with 1800 highlighted in white. Did you then press ENTER? Tip, if you don't have any charts, use the restrictions on the FPLN page as a guide. So you would have a target of 8000 ft for MGW.

Sign In or Register to comment.