What could possibly be more clear-cut than post #12? :)

Thank you! ^

I've never managed to find an "official" document online that simply defines them. But there are many pages on various sites which illustrate it. For example: http://www.jal.co.jp/en/jalcargo/inter/map/

Page 10 of this document, which is on teh IATA website, also defines them:
http://www.iata.org/NR/rdonlyres/DF0...0/Section3.pdf

A follow up question on alternate routing
 

Thanks everyone for your valuable advice. So my sister is finally in the middle of her DONE4 trip! The itinerary was slightly changed because of avilability, etc. as follows:

BOM QF X/SYD QF MEL QF SYD QF OOL //BNE QF PER BA X/SIN BA LON BA MCT BA LON BA NYC AA SFO CX HKG CX BOM

I managed to get it validated by AA and had it issued in India. BA, CX or QF were not willing to issue it!

Now, I have 2 questions:

1. I am unable to get a seat from SIN-LHR on 1st December on BA or QF or via HKG or BKK on any of the OneWorld Carriers in D class. Is there any other routing that can be used to get from PER to LHR without violating the DONE4 rules or using up one of the two UK to Middle East segments.

2. For purposes of the two segment restriction between the UK and Middle East, can you do get between the Middle East and London on a OW cooneecting flight that would not violate this rule?

1. PER-NRT-LHR is a possible route, but there's no availability on NRT-LHR on 2/12 according to expertflyer. If you could stay one day in Tokyo:
QF79 dep 1/12 22:10, arr 21/12 08:45
BA6 dep 3/12 11:00, arr 3/12 14:30
(can't depart PER on 2/12 since it's not daily).

2. No.

But you have a load of spare segments, so how about:

PER-HKG-BKK-HEL-LHR
30/11: CX170 dep 12:50, arr HKG 20:35
30/11: CX709 dep 22:00 arr BKK 23:50
1/12: AY96 dep 12:35
1/12: AY835 arr LHR 20:40

all have D according to EF.

The PER-NRT-LHR with a stopover will not work because it will violate the rules. Can only be done if NRT-LHR is within 24 hours. Also, she needs to be in London on 2nd December. She is already confirmed PER-SIN-LHR on 3 DEC.

The PER-HKG-BKK-HEL-LHR on 30 NOV is too early. She only gets into PER on 29 NOV at approx 6 PM. Defeats the purpose of going to PER. Also on 30NOV, PER-HKG and 1DEC HKG-LHR is available on CX so will not need to do take 4 flights.

Thanks anyway.

I think that under the new constraints posted above your sister will have to either re-route via MEL (D9 to LHR), or take that PER-HKG flight on the 30th, or face a downgrade to economy via NRT or elsewhere, because SIN-LHR is showing not only D0 but L0 as well.