ETOPS Validity/Diversion Window Questions
 

Hi Everyone,

First time posting... apologies if this is in the wrong place.

I am an aircraft dispatcher for a U.S. airline going through ETOPS certification. When it comes to how diversion / validity windows are to be calculated, two schools of thought have emerged and nothing I've found online (yet) really clarifies which is correct.

Scenario is this: Flight from LAX to HNL, with SFO and ITO being the two ETOPS Alternates. They also serve as the EEP / EXP Stations and are an ETP pair. LAX is within SFO's 60-minute circle.

The first claim is that, in such case, the earliest possible arrival time at SFO would be the case where a plane departs LAX and immediately heads straight for SFO. Logically, this is correct. The second claim is that the earliest possible arrival time at SFO is the time from LAX to the EEP, and then diverting back to SFO. These two times differ by more than an hour. The support for this claim is that, until the plane enters ETOPS airspace, it is not subject to diversion windows and is simply a domestic flight following domestic rules. It needs to get to ETOPS airspace (i.e. the EEP) before the rule kicks in, thus the calculation has it reaching EEP before it diverts.

On the other end of the flight, two more thoughts have emerged.

One claim is that the latest possible arrival time at ITO, the last ETOPS alternate, consists of Elapsed Time to the ETP mid-route, plus the slowest scenario direct to ITO. Another claim is that the latest possible arrival time should be Time to ETP, plus slowest scenario to HNL, plus slowest scenario divert to ITO.

Everything I find online demonstrates how to calculate diversion windows based on ETP's between ETOPS alternates, but nothing I've seen so far discusses before the first one or after the last one, or cases when an ETOPS alternate is within 60 minutes of origin / destination. If anyone can shed some light on this, it would be much appreciated.