Too fast-moving for busy people to catch up on all the posts but, having done so, I find only one poster has had almost identical thoughts to me, but the other way round. Thanks Puntosaurus, although I have felt particularly uncomfortable when posting this theory, as I imagine you may have been?
Firstly, a quick update on fuel quantities, as there appears to be a little confusion. Airframes post s/n 250 have slightly larger tanks so, given that SPAO is s/n 546, built in 2007, she will have had supply tanks that read 47 & 43 kgs respectively (the only relevant figures for the moment). This very conveniently comes out at the 90kgs normally used as night Police MLA.
Taking off with 400kgs equates to 310kgs useable to MLA, at 200kgs per hour, that's 1:33ish, plus a few mins if they'd spent a little time in "loitering" flight, rather than a typical max cont transit, with max cont hovers in between.
At a certain stage, they may have found themselves in a high nose-up hover, possibly around 80-100kgs in main tank after 60-80 mins flight, whereupon the fwd transfer pump runs dry, amber warning on CAD, & is switched off, i.a.w. SOP/FLM. No problems, since aft transfer pump keeps supply tanks topped up.
The transit to forward flight takes the remaining fuel down to the forward pump, but something distracts the team from switching the forward pump back on & the aft transfer pump caption soon illuminates, and is also turned off - meanwhile the supply tanks are now feeding the engines and 70ish kgs is indicating in main tank. Now two amber TXFR PUMP captions on the CAD. Plenty of fuel at a glance (if a "glance" at the main tank is all that's absorbed) but it's not in the right tanks. It's recoverable, but needs an appreciation of what's been done after 1:30 in the air, and a good read of the CAD will be required when, & if, No2 winds down as the RH supply tank runs dry. Tired crew, still on a job, lots of captions, and a PC3 aircraft over a built up area well below 1500' and reducing options, reduced further a few mins later while scurrying back to base? Still 75kgs in the "tanks", but which ones? As p3bellows #984 mentioned first, I'd be most interested in the position of the Transfer Pump switches, more than the engine switches. It's a question / theory only, but would very much like to be proved wrong.
And to clear up a few other comments; Whitehead 06 # 1029 - Yes, longer transits and less time doing the job, re #1044 - I'd suggest there's no "normal" when fuel runs out, it "normally" doesn't happen. SCFool #1024 - unless absolutely necessary, pilots will not touch engine controls at any time when airborne operationally. DXWombat # 1020 - As Police radios are digital and coded/secure, and whilst I'm not a radio ham expert, I don't believe they can be listened into at all. Stevo67 #1010 - no, engine switches are on the dash, a long way away from the rotor brake on the overhead console.