January 31, 201511 yr This is probably down to user error and not understanding VNAV limitations but i can't find why this message came up and also VNAV Disconnected. I have provided below a snap shot. I passed waypoint PT405 and started my CDO in VNAV PTH i was at FL100 or just below, my MCP ALT was set at 3000ft my next waypoint was ODLIX and then i got that CHECK ALT TGT. I'm not sure what i have done wrong i only set my MCP ALT to the FAF (3000) and i was on path and FMA was showing VNAV PTH http://www.fsfiles.org/flightsimshotsv2/image/EPu Vernon Howells
January 31, 201511 yr Author https://www.dropbox.com/s/yw60lklz5wnzx64/2015-1-31_17-48-18-397.BMP?dl=0 https://www.dropbox.com/s/sz64d4fuctpj8kp/2015-1-31_17-48-27-965.BMP?dl=0 Vernon Howells
January 31, 201511 yr FCOM 11.60.2 Message is because VNAV disconnect. Not sure if you want to try a 3 deg CDA at 240 KIAS.... might be hard to achieve. Dan Downs KCRP
January 31, 201511 yr Author Sorry about the pics, they are a bit dark! Right, i see! Its because the plane can't achieve a 3 degree glide? Vernon Howells
February 1, 201511 yr Right, i see! Its because the plane can't achieve a 3 degree glide? Depends on your groundspeed f(TAS, Wind). A 3 deg slope is about 318 ft/nm which is easy at 150 KIAS but at 240 KIAS at 10,000 where your TAS is closer to 300 KTS you best shoot for something around 250 ft/nm. Dan Downs KCRP
February 1, 201511 yr Author GS - 298 TAS - 280 Wind 326/42 I can't see why that would cause a VNAV Disconnect? Vernon Howells
February 1, 201511 yr Author FCOM 11.60.2 Message is because VNAV disconnect. Not sure if you want to try a 3 deg CDA at 240 KIAS.... might be hard to achieve. You've picked the post up wrong! I see where you're coming from, its not from the FAF 3 degree glide. But rather from a set location on the STAR. Did you try to re-select VNAV? I done exactly the same flight and descent, this time no CHECK ALT TGT and VNAV DISCONNECT. Vernon Howells
February 1, 201511 yr I done exactly the same flight and descent, this time no CHECK ALT TGT and VNAV DISCONNECT. Maybe a little less tailwind or a little more headwind. Decreasing from 318 to 250 ft/nm changes the angle from 3 to 2.4 deg, which makes it a lot easier to stay on path and is well within the allowable range for the published arrival. Dan Downs KCRP
February 1, 201511 yr Author Maybe a little less tailwind or a little more headwind. Decreasing from 318 to 250 ft/nm changes the angle from 3 to 2.4 deg, which makes it a lot easier to stay on path and is well within the allowable range for the published arrival. You know your stuff how did you calculate that? Vernon Howells
February 1, 201511 yr LOL I spent several years manually keeping about 60 sidstar files up to date. Basic trig: sin-1 (rise/run) = angle; e.g., sin-1 (250/6080) = 2.4 deg. Conversely, 6080sin(3)= 318.21 thus you descend 318 ft/nm on 3 deg glidepath (6080ft=1nm). Given a groundspeed (nm/hr) and a descent rate (ft/min) you can get to a descent rate in ft/min by converting units. Dan Downs KCRP
February 1, 201511 yr Other good (cockpit-friendly) descent maths: required rate of descent for a 3 degree glide = (GS/2)*10 and height for a 3 degree descent = FL/3 (plus any bodge factor for your airframe/winds), or alternatively track mileage to run*3. Simon Kelsey
February 2, 201511 yr Other good (cockpit-friendly) descent maths: required rate of descent for a 3 degree glide = (GS/2)*10 and height for a 3 degree descent = FL/3 (plus any bodge factor for your airframe/winds), or alternatively track mileage to run*3. Works out nicely that 318 is close enough to 333 to do the divide thousands by three shortcut. Dan Downs KCRP
February 2, 201511 yr Author All good rules of thumb there! I have redone that flight from saved points and no CHECK ALT TGT or VNAV DISCONNECT. Vernon Howells
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