B737-700
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 246; Flight Crew Type 5000
Human-Machine Interface; Situational Awareness; Communication Breakdown; Fatigue
Inflight Event / Encounter Unstabilized Approach; Inflight Event / Encounter CFTT / CFIT
Flight Crew Took Evasive Action; Flight Crew Regained Aircraft Control
Human Factors
Beautiful night; last leg into ZZZ; slightly high but configured early with flaps 5 and gear down. Announced and selected V/S to gently get down glidepath for smoothness. RNAV XXL was set up and we were getting vectored for the visual. Airport in sight since ZZZ1. Autopilot on. Good rapport with FO; felt like an easy-peezy; no brainer; in-the-Green arrival. We were cleared to descend to 1;600 feet.1. A few miles from the final approach we were cleared the visual. I announced 'LNAV to XXXXX;' executed direct to the FAF and let the autopilot get us going that way. Kept in V/S. 2. HUD was up and in use.3. We were slightly high so I left 950 fpm descent rate in V/S knowing it would intersect the 3 degree slope near 1;000 feet. We were fully configured a bit early; this was just an attempt to be smooth and require the fewest power changes.4. Disengaged the autopilot at probably 1;400 feet and started following HUD guidance. Little circle in the big circle. It could have been a simulator with turbulence set to 0 for how little control action was required. 5. '1;000 feet; Speed 135; sinking 9.' Little circle in the big circle.6. At some point before the 500 foot call; it dawned on me; ALL FOUR PAPI's had gone red!!! I immediately added power and got back on PAPI and the purple path (VNAV). I never pressed VNAV. The magenta indicator was there but I was on that guidance cue; blindly following V/S into the black below.Obviously I screwed up. We screwed up. I will be changing my own procedure to never use V/S for this purpose on final. It was an eye opener. Would the aircraft have sounded any Warning had we continued? I realize it can't warn for everything; but why not pick the low hanging fruit. It 'knows' where the runway is; it could easily report the unsafe condition. I'll fix my own procedure but let's collectively; as an industry; go to the next step. The was the end of a LONG day; so fatigue was a factor; but this was a super low-stress easy approach. Why didn't the FO say anything? Don't know. He asked the same question when we talked about it afterwards. I've NEVER DONE THIS BEFORE. But the more I thought about it the more it made me think. What if the VASI wasn't there or was inop? We could have easily still done the approach. How much lower would we have gone in a black-hole approach? It was probably the ease of the approach; the mundaneness of it; combined with fatigue; that allowed it to happen. I'd like to propose EGPWS get more E. If this can happen to me; it can happen to someone else. The airplane 'knows' its position relative to the runway in nearly all cases now. If the airplane is in close; within 5 miles; have it report 1) too Low; vertical path; 2) too fast; 3) check runway; and so on.   WE CAN FIX THIS.
Captain reported selecting the V/S mode rather than VNAV which resulted in the aircraft descending well below glidepath on final approach at night. Upon recognizing the runway PAPI indications; the crew climbed back up to glidepath.