Not rushing to judgement is quite commendable but do you not feel there is a level of confusion which should simply never occur when flying a fully functional and instrumented aircraft during daylight hours with relatively clear sight of the ground and moderate haze?

Adopting a track to enter a traffic pattern for runway 20 when cleared to land 02 may be accepted as confusion.

Entering the left downwind when ATC clears you for the right (then right, then right, then left, then right) downwind is easily accepted as confusion, especially when ATC seem to be clearing you for whatever they guess you're planning to do next anyway.

Then they receive and understand 'cleared to hold?' They readback 'right orbit' then proceed to steadily lose height in the orbit until - I'd guess - an EGPWS warning shakes them out of their fugue state. They abort the orbit into an approximate (climbing, of course!) left base leg, overshoot the runway they apparently can't see (probably due to being too high), 180 left turn into... well, it's high key, isn't it? Followed by the usual which turns out not to work so well in an ATR.

I see a lot of confusion in the initial stages, but in the later stages I see a certain 'I know exactly what to do, now I just have to get the airplane to do it' certainty of purpose that's something quite different entirely and much more dangerous. Confused people aren't dangerous if they know they're confused. They hold, they put the autopilot on, they pause. The danger starts when people suddenly snap out of their confusion, believe they're in a familiar and tolerable situation and begin a tactical approach from high key. In an ATR. Wouldn't you say?

Except it was in a Dash not an ATR

As requested METAR

VNKT 120850Z 26007KT 140V300 7000 FEW015 FEW025CB SCT030 BKN100 21/10 Q1015 NOSIG CB TO SE AND S=
VNKT 120820Z 28008KT 240V320 6000 TS FEW015 FEW025CB SCT030 22/11 Q1015 NOSIG CB TO SE S AND SW=

in hindsight a go-around instruction from the tower would not have been a bad thing.

but they probably assumed the plane had some kind of problem and didn't want to add to it.

Thank you. So there would appear to be no weather problems over the airfield. Reasonable visibility with circuit level dotted cloud and light winds. So why did the straight in not work? The root cause lies well before the chaos of 'buzzing the tower & apron' in a seemingly 'where am I and what am I supposed to do' quandary.

Apart from the specifics of this particular accident, how many countries are there in the world that allow scheduled VFR flights in transport category/heavy turboprops?

Captain had landed 100+ times at this airport.
All very strange.
Seeing the final track and the tightening left turn I actually wondered if something was amiss w the left engine right at the end.

Hypoxia
 

I still lean towards some sort of hypoxia incident here, and I wouldn't normally jump straight to that conclusion as there should have been plenty of warning signs.

However if you are hypoxic, might not recognize them. Although the masks would have dropped based on cabin altitude if that was the case.

Even though I just speculated I'm not a big fan of speculation in aviation so FDR/CVR should help here.

We can all speculate until the cows come home. There comes a time when speculation needs to give way to some patience for the facts to emerge.

FYI most Q4s don’t have drop down masks in the cabin it’s an optional extra for max ceiling of FL270

Also we cannot talk about track that drawing/sketch is purely made from eye witness accounts would say it has very very little accuracy.

Does KTM have radar? If not any military stations? be nice to see a radar track

Possible "fuming incident"? Loss of situational awareness....

Just my two cents

You know, I've started flying to VNKT in a heavy pretty recently. I do it regularly now. It's a Capt's landing and take off as per my company SOP's. After my first two approaches there, where I found myself 'busy' mentally, with FO's from a culture that have a hard time speaking up to and correcting the Capt. (no- I'm not an a....in the cockpit) I decided to let the FO fly the approach the last few times. My reasoning; I want to be 100% concentrated on exactly where we are and what comes next. And not be busy pushing buttons. I've found myself much more at peace and ahead of the game, going into VNKT, monitoring and guiding the approach, in min. weather at Kathmandu. Breaking the SOP's? Yes I am.:ouch:

Looking at the path it seems to me a reasonable explanation is a series of attempts to circle to land on 20... none of them are good and seem to have been affected by too tight/maybe fear of terrain,

As it goes on the excursions get bigger and the turns tighter

probably finally total loss of awareness (but still fear of nearby terrain) and overcooks the turn and stalls in

I agree with that. But it doesn't seem that there's an obvious problem (i.e. declaration of emergency) that warrants flying something without requesting it first, or at least a short while after starting to doing it (that last bit as a sort of a benefit of doubt in case of a hectic cockpit for whatever reason). ATC is the first to notice they're deviating from their clearance. IMO they failed to do any of those three "golden rules" in a proper manner. They shouldn't crash if they've done them properly, but FWIW, initially at least, I think they attempted to aviate but failed to navigate and communicate (efficiently anyway).

@eternal: I don't get it mate. Why would they suffer from hypoxia (at 5-6k ft anyway!) and, based on what has been said here, after a considerable amount of flight time (around 1hr). Plenty of things should have happened before if that was the case.

My first questions would be:
- What happened with the first approach? Everyone else seems to have managed it. There isn't an obvious sign of why they botched/missed it
- What happened in the cockpit after missing that first approach, regarding decision-making, PF/PM duties?

Everything else after that I think is just the consequence/poor execution of these decisions/actions

Having read the transcripts and also the comments relating to slurred speech, confusion, and erratic communication combined with the miss handling of the aircraft it struck me the pilot flying may well have suffered a medical problem, specifically the possibility of a TIA (transient ischemic attack) prior to and during the approach.

Sometimes Occam's razor can cut.

In all the cases where people have suggested incapacitation, fumes, hypoxia etc in order to explain otherwise inexplicable flying, I don't think a single one has been found to involve such an event after the formal investigation.

The simpler explanation is that the human brain is fallible, gets overloaded, loses SA and never regains it. Remember that these are rare 1 in 10 million events, most pilots will never experience such a degree of mental "lockup" through their whole career.

Really good post and points

I think you are right - I've "locked up" once and seen it happen to others (all in non-flying/driving situations thank God)

Its very weird and normally caused by the brain just getting so much conflicting information WHEN KNOW YOU NEED TO REACT FAST -you just shut down,... might be 10 seconds, might be 15 minutes........... You remeber what was happening - you just can't make any decisions

Kindred spirit - good decision.. Never understood the bull**** of Captains Only airfields. Captain can make the decision about who is flying but if they can't make that decision in the best interests of the flight they shouldnt be captain!

"bull****" well the regulatory body of the airline most certainly won't see it that way....

Nor will the insurance company.