For those doubting that 2 'experienced' pilots, fully alert and with an a/c operating normally in good weather (let alone bad weather at night) could ever find themselves in a situation where they allow the a/c to slow to a potentially dangerous airspeed by forgetting to add power, allow me to impart some first hand experience.
I did exactly that, in a Q400, approximately 2 years ago, and until then, I would perhaps be equally scathing about such a scenario.
I was the handling pilot, flying a short inter-city sector on a pleasant summer day, and as we approached the holding point for the STAR we were flying, were instructed by ATC to take up the hold. Simple enough. Prior to this, the ATIS had been received, the brief given, and the STAR, hold and arrival programmed into the FMS. A/P was engaged.
As we entered the hold, descending to our cleared level at approx 800fpm, we were informed that the arrival runway had been changed. This necessitated a re-programming of the FMS. For some reason I do not recall, the non-handling pilot was having some difficulty doing so, and rather foolishly I allowed my attention to be distracted from monitoring the a/c and assisted.
Predictably, just as I did so, the A/P captured the selected level, levelled off and continued to fly the hold. No problem at all really, except for the fact that as there is no autothrottle, power was set at a level just above idle. The Q400 is a slippy beast, so it took a short while for the speed to decay significantly below 210kts, but once below perhaps 180kts or so, it decays very rapidly indeed.
As both myself and the other pilot were both heads down, leaning forward in our seats, the increasing deck angle was not immediately apparent. Fortunately, I happened to notice the lack of noise and a seemingly unusual attitude, and immediately recognised what was happening. I set climb power and the a/c responded instantly. The IAS had dropped to something in the order of 150kts!!!
From levelling off to reaching our slowest speed, the whole process had taken perhaps 30-60 seconds, and it took perhaps 10 secs to restore 210kts. It seems incredible looking back that I could ever be so dumb as to find myself in that situation, but it happened anyway. More worrying still is that until the power suddenly increased, the other pilot was equally oblivious to the developing situation.
For the poster earlier who enquired as to what the deck angle would have been, I'm sorry but I honestly couldn't say for sure (perhaps 8-10 degs), but it was sufficiently steep that after recovering the a/c we received an enquiry from our senior CC to ask if we had performed a go-around. She knew we had been descending (the cabin was already secure), felt the a/c level, then noticed a steepening deck angle and then a large application of power. In the cabin this probably felt just like a climb.
Both myself and my even more experienced colleague were very, very, very fortunate to have done little more than learn very valuable and basic lessons that day, but please don't sit there and tell me it can't, doesn't or won't happen in a multi-crew environment.