Airborne_Again wrote:
Trivia: The remarks sections of some METARs include the QBB code which I’ve never seen before. According to Wikipedia it means the cloud height. It was used in METARs giving vertical visibility instead of cloud so it makes sense.
Yea Russia use some unusual to us codes. I remember dispatching airplanes through there and it was always intersting to see what was there. Brings back memories of the Q codes… Mind, and further OT, not 10 years ago I encountered a Synop station here in Europe which still had to send their messages using a morse code key via land line. They also used q-code quite heavily for everything. I guess that may have changed by now as well.
Peter wrote:
Nobody is going to install three AIs in the primary field of vision – there is no room.
We have something close to that in the TB10. Vacuum horizon upper middle in the six-pack, G5 below it, turn coordinator to the left of that.
Mooney_Driver wrote:
clear case for a third one: Let’s say you are flying at night, normal cruise, and your primary fails gradually, starting with a small bank. You correct, but it won’t follow. You have one more, but due to spatial disorientation, you need time to figure which one is right, so a third one, which can verify that, is a big help. ADI failures at night without backups have in the past cost a lot of lives. Particularly but not specifically in the military. There have been cases even in airliners, where crews followed the wrong ADI into hell, because they did not compare the two others properly. So I would suggest, for GA they should be pretty close together, unless you fly dual crew, where it is very useful to have one in the copilots side.
This is why, if in IMC and not actually flying an approach, I switch the G5 (in the usual DI/HSI position) to AI mode. You still get the heading and track information that you need, but also two AIs arranged vertically right in the middle of your view, so it is really obvious if they start to disagree. Much more apparent than disagreement between AI and TC in the traditional setup. If they start to diverge, you check the TC and decide where to place your bets.
Not sure how useful a TC would be near the ground, just after liftoff, when you may enter a roll but not yet producing a roll rate.
I have seen a vacuum AI (the KI256 installed per STC) with an electric AI next to it. Rare though.
Peter wrote:
Not sure how useful a TC would be near the ground, just after liftoff, when you may enter a roll but not yet producing a roll rate.
How can you enter a roll without producing a roll rate? Do you mean yaw rate? That’s not necessary with a TC (but it is with a T&B).
By tipping the plane 
It will continue the trajectory… until it doesn’t. Then you die
But, seriously, for low IMC deps you have to keep the wings level, definitely. It needs an AI.
Peter wrote:
By tipping the plane
Right. And to tip the plane, you have to have a roll rate which the TC will indicate. That’s why TC’s are used rather than T&B as backup instruments.
Well a TC does what it says on the tin, and beyond rate 1 the information is just binary, ie you are turning more than rate 1, with no indication by how much.
This is why in a spiral dive you roll to opposite rate 1 and then back to wings level. In effect resetting the parameters where the TC is useful. A spiral dive with a bank approaching 90 degrees or more, rolling just level might leave you still in a 60 degree bank, but not turning, and the TC will show wings level.
The T&B or bat and ball has the virtue of showing spin direction in all attitudes, while the TC struggles during the forces of autorotation.
RobertL18C wrote:
… in a spiral dive you roll to opposite rate 1 and then back to wings level. In effect resetting the parameters where the TC is useful. A spiral dive with a bank approaching 90 degrees or more, rolling just level might leave you still in a 60 degree bank, but not turning, and the TC will show wings level.
The reason why you have to “overcorrect” when recovering from a spiral dive using the TC is that the TC also indicates a roll, so it always overreads in the direction of the roll. This is beneficial when using it to fly straight and level (which is why it is built that way to start it), but when using it to roll out of a steep turn with a high roll rate, it will indicate “no turn” well before the wings are level. This happens when the remaining yaw from the turn and the roll rate out of the turn are roughly equal. The higher the roll rate, the more pronounced the effect.
If you still have a 60 degree bank, unless you have a massive rudder against the turn or absolutely no lift on the wing, the aircraft WILL be turning.
while the TC struggles during the forces of autorotation.
The forces have little to do with it – but autorotation is a combination of yaw and roll. In an upright spin, the yaw and roll are in the same direction, so the TC will read correctly. In theory it overreads the rate of turn, but in reality it will be pegged at the stop because spins tend to be significantly quicker than 2 minutes per revolution…
In an inverted spin, the yaw and roll are in opposite directions, so the TC will underread or even read the opposite direction, depending on how developed / steep the spin is.
Peter wrote:
I have seen a vacuum AI (the KI256 installed per STC) with an electric AI next to it. Rare though.
I thought it was a pretty common setup in Germany. My N-reg plane that I bought from Germany has exactly this setup.
Graham wrote:
Much more apparent than disagreement between AI and TC in the traditional setup. If they start to diverge, you check the TC and decide where to place your bets.
The problem is that quite a few EFIS airplanes don’t have a back up TC. So if the EFIS is dead or degraded, the TC is gone with it.
Maybe one of the “perks” of having an S-TEC AP is that it forcibly needs a TC to work. Some people hide it behind the panel. Which I consider a waste. If you have it, drill a hole and display it. Might save your life.
