IREX KDR question

[Canicoll]

I passed my IREX by a whisker and now I am going through the KDR questions and I have one that I am unable to answer. I can't seem to find any information on it but that could be due to a fried brain right now.

4. Operational planning requirements
4.2 Alternate requirements
4.2.1 Describe the alternate aerodrome requirements for the following:
(e) Divert time

The question seems a little ambiguous and I can't find anything on Divert Time.

Appreciate any help if anyone has seen this before.

[The Green Goblin]

This will be referring to a take off alternate. You are required to have (when conditions don't allow a return to land at your departure aerodrome) an alternate within 60 mins single engine flight time. Practically you could use your blue line speed as a reference (on a light twin). Then have an alternate within that many NM. If your blue line speed (vyse) is 106 kts, have a suitable place to land within 106nm.

Being even more practical, you're probably best in most light twins to sit on the ground if the conditions are below landing minima. If you have an engine failure, the other one will more than likely take you to the crash site :)

[Canicoll]

Thank you and it's interesting you say that. I actually wrote down the alternate must be within 60 minutes flight time but I have no idea where I read that.
It feels like i've been through the Jepps and AIPs a thousand times but I can't find any reference to it.

Thank you again for your reply.

[Mach E Avelli]

Look in CAO and CAAP for EDTO. It appears that the question could relate to this, which is a bit deeper than just the takeoff case. However they could have led you in the right direction by stating that the operation was charter, turbine, number of engines etc. etc.

[Nomde plume]

I believe 'divert time' may be referring to the concept of 'latest divert time' whereby you're given a scenario such as:

'You are holding at YAAA due the the weather being below landing minima at time 1300Z, with 70 mins fuel on board. Alternate YBBB is 25 mins flight time away. What is the latest time you can hold at YAAA until you divert to YBBB with reserves intact?

The 60 minute rule you refer to is for NVFR aircraft planning to an aerodrome not served by a navaid. AIP ENR 1.1 58.3.3

[scavenger]

Nomde Plume has it - ignore the first 2 answers ITT for IREX.

Don't forget to account for reserves, including VR if it's CHTR.

[rip_vhbdb]

I believe 'divert time' may be referring to the concept of 'latest divert time' whereby you're given a scenario such as:

'You are holding at YAAA due the the weather being below landing minima at time 1300Z, with 70 mins fuel on board. Alternate YBBB is 25 mins flight time away. What is the latest time you can hold at YAAA until you divert to YBBB with reserves intact?

The 60 minute rule you refer to is for NVFR aircraft planning to an aerodrome not served by a navaid. AIP ENR 1.1 58.3.3

So how would you answer it? I had same KDR for this question and I figure 25 min flight to leave reserves intact you have to divert now in this scenario, 70-25 = 45, I believe question was essentially the same in exam being time to alternate left you right on min fuel

[scavenger]

Yep, there is no VR required on alternate fuel in IREX anymore (VR is calculated on the trip fuel only, and only for RPT/CHTR), so the latest divert time in your example is now i.e. 1300

Be careful as the alternate may have its own holding requirement due weather, lighting or traffic - all of which would make the latest divert time earlier.

This isn’t a well constructed question as the fuel on board minus the FR exactly equals the flight time to the alternate. Normally the questions in the IREX would have a latest divert time sometime after the initial conditions are given.

To your point though, yes, it’s latest divert time and in IREX there’s no requirement to include time for approaches at the destination or alternate. So start with the required fuel on board arriving at the alternate (any holding plus FR), add the flight time to the alternate, then subtract the result from the current fuel on board. The result is how long you can hold at the destination before diverting.

[Checkboard]

What’s “KDR”? :)

[Ascend Charlie]

KDR = Know the Dumb Rules


It is one of those convoluted things that the air-heads think up to make themselves think their job is important, so instead of saying "You got these wrong" it comes down to a "Knowledge Deficit Report".

[Checkboard]

Ah. After my time, obviously. Sorry to interrupt.

[zanthrus]

AC. You had me snorting my coffee re your KDR definition. Gold! 👍🤣