Only for underspeed, and then only on the edge of stall (assuming the NGX modelling of the AP modes is correct). So if you select excessive rate of descent the aircraft will overspeed, and an excessive rate of climb will cause airspeed to decrease until it reaches minumum. Then you are well on the wrong side of the drag curve and the aircraft will probably be losing height, not climbing.Kevin Hall

You're at Vs1.3, just like Vref, so you probably won't fall out of the sky. I wouldn't plan on using Min Speed Reversion, but it does exist.

We have FLCH in the 5 and 550 also. Just as Kevin stated, it's alot safer to use lvl change during large climbs and descents. I love it for the speed protection. VNAV will over speed the jet if the descent path is too steep. In vert speed, you have to keep an eye on your speed during climb and descents. This becomes distracting in high traffic areas, during storm dodging, and heavy ATC vectoring. You look up and suddenly you are slow or fast when you was just fine a moment earlier. I will say that lvl change gets inconsistent after mach change over in the climb. The jet starts to hunt and porpoise as it tries to keep the mach. The DC-10 would do the same. The 550 is more stable. At this point i use vnav or vert speed. I prefer vert speed after takeoff because FLCH causes a high deck angle which leads to my principal spilling his/her drink. I also like vert speed for slowing prior to passing 10,000ft. I set 1200fpm at 12,000 and she hits 10,000 at 250 clean. Once at 250 i select FLCH and i vnav or vert below 5000. Getting far off your target speed can be embarrassing.

Got it. Thanks for everything!