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View Full Version : 737 NG Glide ratio and best glide speed for ForeFlight app


sire
24th Jul 2018, 01:19
Our company just approved the ForeFlight app as a backup to the JeppFD-Pro.
One nifty thing in the ForeFlight app is a "Glide Setting"
You put in the best glide speed and the airplane glide ratio and then the app will show a circle around you airplane symbol on the map showing you how far you can glide engine out. With a strong wind this circle is elongated.

Does anyone know what the 737NG best glide speed and glide ratio would be. -700 and -800 and MAX (gave away where this is....)

sierra_mike
24th Jul 2018, 09:24
your best glide speed is weight-dependent and the difference can be quite significant among the range from MTOW to an almost empty ship. i'm not 737 rated but i would assume you can find the speeds in something like a dual engine failure checklist.
glideratio on the other hand is constant (for a given configuration) and i'd guess it's at least in the higher 1/20s or maybe even above 1/30 for the MAX (clean).

Themax23
24th Jul 2018, 10:23
The Loss of thrust on both engines checklist actually asks you to dive at high speed (275kts above FL270 and 300kts below) in attempt to restart at least one of your engines. This glide circle is initially useless in that case.

sierra_mike
24th Jul 2018, 11:01
how about a table for OEI in cruise driftdown speeds? usually aims for minimum altitude loss at MCT. that should be around best glide as minimum holding speeds should be as well

Warped Wings
24th Jul 2018, 14:05
Best glide speed in the 737 is the driftdown speed which will vary with weight (anywhere from about 210 to 250kts near MTOW). Available from the FMC (CRZ page > ENG OUT > LEFT/RIGHT ENG) or the QRH Engine Inop Driftdown Speed Chart.

If I wanted a real time cockpit presentation showing my chance of reaching an aerodrome, I would put the aerodrome being considered into the fix page (if not aleady on the ND), then select the altitude on the MCP at which I would like to reach the aerodrome (worst would be the aerodrome elevation). The green "altitude range ring" (green arc) on the ND will then give you a real time indication (based on actual VS and GS) of the postion at which will reach the MCP altitude .If the arc remains between you and the aerodrome, find somewhere closer!!

You would be lucky to glide further than a 3 times profile in most instances so I would think that 3 times your current altitude (eg FL300 = 90nm max glide range) would be a good starting point to eliminate aerodrome that are likely to be too far away.

And I hope I never have to put the theory into practice!!

sire
24th Jul 2018, 19:35
Thanks so far for all the answers.
I ask the question just to “play” with it. I don’t think I would use the circle to rely on it to make an airport.
Many more factors involved in a 737 than in a 172, where the circle thingy might come in more handy in actual usage,

73qanda
25th Jul 2018, 11:02
Best glide speed in the 737 is the driftdown speed which will vary with weight (anywhere from about 210 to 250kts near MTOW).
Spot on. From the manual for 737-800SFP
70T= 247
65T = 238
60T = 229
55 T = 219
50T = 209

I’ve played with it in the sim, it appears to be accurate.