threeighteen

SkyWest CRJ is not RNP capable, so the only option is VOR or a GPS over-lay of it. Minimums for it are pretty high at 2300' MSL (1823 HAT), so 2300 would be spun into the ALT SEL. If the Minimums were 2305, 2305 would be set in the MDA window, but 2400 would be spun into the ALT SEL and the AutoPilot/FD would level-off there. One could hand-fly down to 2305 if desired. With the autopilot on, the CRJ will level off above the minimums since the AutoPilot/FD can't be programmed to level off at an altitude that doesn't end in "00."

Adlerdriver

Okay - thank you both.
A better follow up from me would be would they fly a VOR approach (with straight-in mins) like say, VOR 26L/R (KLAS) or LOC 27 (KSAN) differently than that circling VOR in PSP?
i.e. Different altitude selected in ALT SEL, Different vertical mode, procedures, etc.


Or is this all moot because we're talking about an aircraft that doesn't have VNAV, PROF or whatever someone wants to call the ability to program a vertical path?

zondaracer

For straight in minimums on a VOR/LOC/VNAV approach, we will add 50 feet to the MDA and we call this the derived MDA. Prior to the final approach point, we calculate the descent rate based on ground speed and the descent angle. At the final approach point, we descend at that calculated descent rate and execute a missed at the derived MDA. The momentum should take you no lower than the MDA on the missed (thanks to the 50’ buffer).

The CRJ does have advisory VNAV and will display a calculated descent path but this is for situational awareness only, and it is only available with an RNAV approach or if you are using the GPS overlay.

Adlerdriver

Yes, we call it a Derived DA - DDA (since we use it like a DA). We can use published MDA as a DA without the 50 ft buffer in a few specific cases. One being LOC approach with G/S OTS - as opposed to having no published ILS and just a LOC.

Another question - sorry, just being a geek tonight: It sounds like you're coming down in V/S or maybe FPA as you approach the derived MDA. Is that what you have in the ALT SEL? In other words, if you do nothing approaching that altitude, will the a/c level off at mins or continue down toward the runway?

I ask because when we used to do something similar in the MD-11, it would level at mins. The problem was, since you were already basically on glide path, if you let it start leveling off, unless you reacted almost immediately, it was going to be very difficult to get it back onto glide path. So, if you had to go right to mins to break out, you needed to disconnect the A/P no later than 200' prior to the DDA so you could stay on glidepath. Now on the 777 (and I think they changed on the MD too), you put runway elevation in the ALT SEL window so it keeps going down and you have to intervene to go missed (like an ILS) which makes much more sense since you're using a DA just like an ILS.

zondaracer

We descend in VS mode, and in the altitude select we have the missed approach altitude set. At the derived MDA, if we go missed, we disconnect the autopilot and fly the missed. If we continue to land, we disconnect and the plane is usually trimmed out to continue down the descent path.

foumanchu

At the company I fly for (CRJs), we put the DDA(rounded to next higher 100') in the ALT SEL to get a descent started in VS. We then twist the missed approach altitude into the ALT SEL window after descending past the MAP alt. We get the minimums call at the DDA from what is set in the MDA, but the aircraft will not level off.

My original posting was concerning a different aircraft. The profiles that someone has established for it don't make sense to me.

One profile is along the lines of the dive and drive, but it has a derived MDA. The reasoning in this case is that the Autopilot might overshoot so they added the autopilot tolerance into the MDA and then round up.
That doesn't make sense because the purpose of having a derived altitude is to fly the non-precision like a precision with the added buffer.

The other profile is close to a continuous descent final approach, but then it doesn't have a derived MDA/DDA. Neither of the profiles that have been established seem appropriate.

Adlerdriver

We're coming down in VNAV the whole way, possibly from the IAF or even a feeder fix in order to hit all intermediate altitude restrictions on the approach. So, if we set MAP altitude and it's lower than the IAF or even FAF altitudes, it's going to capture on the way down the approach. Since we're VNAVing all the way down to the DDA (or DA on an RNP) we have to have something lower than all the altitudes on the approach including mins set in the FCP window (ALT SEL). So we can't set MAP altitude in the window until we actually make the decision to go missed.

You're right, that MDA plan doesn't really make sense considering you're never going to actually level off at mins. You hit the Derived MDA and you go missed. There's no point in buffering an altitude (due to A/P limits) that you're never going to actually level off at.

FlyPurdue

I wish we did ‘CDFA’ on the 145s at Envoy. I repeatedly asked if dive and drive (while leveling out at each intermediate altitude no less) was really how we did LOC/VOR approaches, and was looked at like I had 2 heads when the instructor responded with a resounding ‘yes.’ So many opportunities to get slow/unstable.

To answer the question, we round up the MDA to the nearest 100 feet so we can put that in the altitude preselector.

galaxy flyer

Does your planes have a VGP function for Baro/VNAV approaches, where upon path capture, VGP shows on the FMA, the ALT Selector becomes inactive and is set to missed approach altitude?

gf

FlyPurdue

Hi GF, I’m not sure whom that was directed to, but we did it at ExpressJet just like a poster above referenced at SkyWest; by adding XX feet to the MDA, and computing a V/S based off of GS. Here at Envoy it is a pure and simple Dive and Drive. Our RNAV approaches have a pseudo GP, but we only use it to LNAV minima.