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Greg Goodavish

Cold weather starts with PSS 777

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I am able to start up this aircraft with the checklist with no problem in warm weather. I have discovered, though, that in cold weather (-10 C or lower), the engines won't start using normal procedures. I even tried going to an airport, having the temp above 0 deg C and started an engine with no problem. Then I changed weather to -10 deg C. I could not start the other engine. What should I do in cold weather?

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This seems to be an issue with both the 777 and 757. I've asked PSS to verify this but so far I've had no response. As to what you can do, do what you're doing now - change the air temp, start the engines, change the air temp back to where it was.Mark

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Interesting. I just noticed the same thing today when I tried to start her up at Moncton where the OAT was -13C. The GE90s made 3 or 4 attempts to ignite, but couldn't. I noticed N2 never made it above 23.7 at that temp. Once I set the local temp to -8C, the engines fired up as N2 crept above 24.0.PSS - Is there something else we can do other than raising the OAT?

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Had the same problem as well in a flight from Denver. Temperature was -14. Had to manually adjust the temperature. As soon as I did, the engine sprang to life.there was something else I noticed. When I set the Take Off thrust setting in the FMC after setting the temperature back down to -14, the N1 setting for TO-1 was over 700%! The only way I could get it back down to a sensible number was to enter an assumed temperature.I think this will have to go in yet another email to PSS as they don't seem to pay too much attention to the forum anyomre.

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The more I look at the N1 limits in the 777 the less realistic they appear. Superficially they look fine until you go away from ISA conditions and start inserting assumed temperatures.Kevin

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PSS - Is there something else we can do other than raising the OAT?-- Offhand no, but I will mention it at the meeting this week, along with the other items I commented on a few days ago.

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Would it be possible for a post regarding what is said and decided at this meeting? I think I speak for a few people when I state that PSS has kept us in the dark for too long regarding bug fixes and updates.

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I'm amazed you are only just raising the problem now. It was first reported late last year.As for what can you do? Try some experimentation, as I have.I found the 777 will start in cold weather if you disable Autostart. RPM does not quite rise high enough to trigger fuel on as currently programmed. With autostart off, fuel can be manually switched on. Fuel control in autostart needs to be fixed.Older PSS products seem to start engines OK in the cold, except the A330, which struggles, sometimes starting, sometimes not at -20 deg C. The default 737 has no difficulty with low OAT, so it's nothing to do with default modelling. Even at +15 deg C the 757 takes a long time to light up. Maybe someone tried to make the start times more realistic, and ended up making them infinitely long when the max motoring RPM was lower (e.g. cold day).Starting fuel flow does seemoveral very low (300 lb/hr or less, depending on N2). I wonder if FS9 has a minimum fuel flow for light off? Most jet engine fuel control units have a minimum fuel flow, usually around 600 lb/hr, which even so is usually less than the start flow.Kevin

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Good spot Kev, although I noticed that all the engine gauges spiked when the engines come to life like the default aircraft when autostart is off, before settling down to their normal levels.

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Phil,I hadn't noticed much difference in the default like spool up behaviour whether autostart is on or off. Seems to be an area which PSS don't pay much attention too.To be fair to PSS, very few add-ons show anything like realistic engine starting characteristics.Kevin

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For the short term no, but I do envisage being able to make a welcome post in the near future.

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I found that if you start the 757 per the check list it will start in cold weather, however; when you push up the fuel valve it will take up to a minute for the engine to finly catch the fuel and ignite, as if it has to warm up for a bit. Just be patient and it will ignite on its own. Per check list: Packs off, R or L starter ingaged (GRD) 20 on the EGT (not to exceed 21) fuel level engaged, wait about 1 minute and it will ignite on its own. Once both engines are started packs on apu off lights as required and off you go.

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The PSS 757 is pretty variable in how it starts at low OAT. I found sometimes it would start, sometimes not, depending on what N2 it cranked to, amongst other things. I think someone made an attempt to make overall engine start times look right by increasing the minimum N2 for ignition to just less than the maximum motoring N2. At standard day conditions this looks OK, but the model just doesn't work at low OAT, because the N2 doesn't quite get there most times.You would not wait 1 minute in the real world with fuel and ignition but no EGT rise. The start would be aborted long before that.Kevin

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777Yes - a good spot and certainly some early rw jets needed the odd work around to start in extreme weathers [although I doubt the 777 falls into this category].757Seems to have a limit of -6C. At this temp its starts ok but, on my installation, at -7C it refuses to light up no matter how long the delay.John Rooum

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Dear friends,I've just remebered that similar situation accured in ERJ145**.The solution was changing in erj.ini, section Engines desription groundFuelValve to 22.0 instead of 24.0.Now, I'm at work and can't check this. I do realy know even is there file *.ini and Engines section in 757 PSS. But, maybe someone could check it.RegardsGwidon

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