Engine out / Decompression ETP's/CP's

[jalbert]

I am probably missing something but can someone explain the point of determining separate ETP's for the engine failure or decompression/emergency descent cases?
I thought that as the failure is assumed to occur at the normal ( ie. everything working as advertised) ETP then there would be no difference in the time taken to continue or return at the reduced speed corrected for the wind .
I guess what I mean is will or how will the ETP's differ for the above scenarios?
Any help greatly appreciated.

[Chimbu chuckles]

Different fuel flows/True Airspeeds/Ground speeds for the two cases.

Chuck.

[Capt Claret]

jalbert

Consider the following scenario.

Norm Ops - TAS 400, HWC 50 kts
Asy Ops - TAS 330, HWC 50 kts
Sector - 1000 nm.

Therefore:

NGSO - 350 kts
NGSH - 450 kts
AGSO - 280 kts
AGSH - 380 kts

Normal Ops CP > 1000/800 [TAS x2 or GSO + GSH] = a factor of 1.25.

Asy Ops CP > 1000/660 [TAS x2 or GSO + GSH] = a factor of 1.515

Time from CP to Home or Dest = 1.25 (or 1.515) x 60 Dist from CP to Dest = 1.25 )or 1.515) x GSO Dist from CP to Home = 1.25 (or 1.515) x GSH

Now just plug in the the appropriate values and you will find that: Norm Ops CP is 437.5 nm from Dest Norm Ops CP is 562.5 nm from Home Norm Ops CP is 75 mins from either Home or Dest

However: Assy CP is 424.2 nm from Dest Assy CP is 575.8 nm from Home Assy CP is 90.9 mins from both Home and Dest

So if blogs the pax has a heart attack and thus a quick landing is required, at normal ops anything further from Home than 562.5 nm means it is quicker to continue than return.

However should bloggs have his heart attack whilst Asymmetric, the CP moves to 575.8 nm of Home, some 13 nm further along track.

This example doesn't consider the possibility of having to chose a lower level due Asy situation.

Stronger winds or a greater diff between Norm & Asy ops will cause the CP to move more.

(ETE @ Norm CP = 96.4 mins. ETE @ Asy CP = 98.7 mins)

[ 07 August 2001: Message edited by: Capt Claret ]