You take a deep breath and ask the captain why he is choosing to do the NDB approach and not the GPS approach. He looks at you quizzically and says that he feels like doing the NDB approach. You point out the lower minimums and straight-in landing available on the GPS and he simply snorts. He finally responds by turning to the approach plate for the GPS. “Listen sport, look at this approach, it takes us over higher terrain to the north of the airport, so we can't descend as early, and we end up going down a narrower part of the valley where the wind funnels more and we get more turbulence. Besides, the wind is out of the north today, so we would have to circle for the Runway 33, and couldn't do the straight-in regardless.”

You have done the GPS approach into the airport before and haven't noticed any of these problems, but he obviously has had some experiences that have made him prefer the NDB approach. You suspect that it is what he is used to doing. The captain doesn't seem inclined to give you an approach briefing, so you look over the approach plate yourself.

A no-procedure-turn approach is possible if you went directly to the VHF onmidirectional range (VOR) and flew over the two non-directional beacons (NDB) en route to the airport. This brings you over the airport at about 1 000 ft AGL, which might not be enough in today's weather. You are approaching from the northwest, making the full procedure approach slightly shorter, but less comfortable for the passengers because of all the turns required. You haven't done this approach before, so you don't know what the captain is planning, but you note that he is tracking directly to the Telkwa (TK) NDB. You are now within 25 NM of the TK NDB so your minimum altitude is 8 900 ft, but you notice that you are descending through 8 500 ft already. You point out the discrepancy to the captain and he simply nods and keeps descending. You are becoming very nervous as you descend further below the minimum altitude, into mountainous territory. You put on your most assertive voice and demand that he climb immediately. The captain chuckles and tells you to relax. He assures you that he has done this many times before and it is perfectly safe. He explains that, thanks to GPS, he knows exactly where he is and he points out that the highest spot height in this area is at 5 700 ft. His procedure is to descend to 7 000 ft until he is about 3 mi. back from the NDB, at that point he turns to the outbound heading and descends to 6 500 ft. When he turns inbound and intercepts the inbound track, he descends in accordance with the approach plate.

You look at the plate and can see how his plan would work, but you also know that it is a complete violation of the approach procedure. You think it might be safe, but the fact that you cannot be sure makes you feel very uncomfortable. What do you do?

Assertively insist that the proper procedure be followed.

Go along with it.  He has done this before, and he has been around for a long time so he must know what he is doing.