Hi Guys: I have had perfecto landings only using CMD "A" VOR LOC and APP mode, whats the big deal about using CMD "A" & CMD "B" am I doing something wrong or odd not sure, thanks.

Hi Guys: I have had perfecto landings only using CMD "A" VOR LOC and APP mode, whats the big deal about using CMD "A" & CMD "B" am I doing something wrong or odd not sure, thanks.

I have been doing the same out of forgetfulness. I haven't seen a big difference.

i think it's more for a back up. in case cmd a fails, cmd b will be engaged to take over without loss of control. Mitch Bowman

i think it's more for a back up. in case cmd a fails, cmd b will be engaged to take over without loss of control

Yes. System redundancy.

Yes. System redundancy.

So it isn't incorrect to land on CMD A Zach?

Its illegal, but it wont matter in FSX.

Its illegal, but it wont matter in FSX.

Hmm, Interesting.

Most carriers don't have fail passive operational systems, by the way and 99% of landings are not autoland - at least not in the US. Most US carriers arm only A if it's the Captain's leg or B if it's the FOs leg. No need to do 2 channel approaches unless you're going to do an autoland. [Thanks for the correction, Tabs.]

From what I understand, by using CMD A and CMD B, the FMS will automatically use the most accurate of the two inputs, if one starts giving bogus information during an autoland.

Great responses guys

But is it normal to have perfect autolands in single channel?

But is it normal to have perfect autolands in single channel?

Are you asking if a single-channel approach will do an autoland? If, so, no. There will be no flare and no retard of the thrust.

Most carriers don't have fail passive systems, by the way and 99% of landings are not autoland - at least not in the US. Most US carriers arm only A if it's the Captain's leg or B if it's the FOs leg. No need to do 2 channel approaches unless you're going to do an autoland.

Actually backwards - most NG operators do not have the fail operational system and do have fail passive. Any 757, 767, 777, 747-400, Airbus etc are always fail operational, so overall fail operational is probably more common.With regard to the original topic, a single channel approach is not an autoland, you're basically just flying straight down into the ground, there's no FLARE or ROLLOUT modes. Plus in the real world this would be a huge violation because you have no redundancy in the autopilot channels.

Actually backwards - most NG operators do not have the fail operational system and do have fail passive.

That's what I said. . . now let me go edit that other post. . . Like I said, I've heard that JAL has fail operational on their 737s, but I don't know of anyone else.

All non-precision approaches and IAN approaches can use only one channel! Dual channel is only available on an ILS approach and full (fail op) autoland only used when localizer aligned with runway centerline. There is no violation to my knowledge to use non-precision approach technique even on ILS. Cat I, for example does not require 2 channels. Cat II also can be completed with only 1 channel (but routinely 2 are used for "redundancy" as stated by prev post). This is all covered in great detail in FCOM.