I'm surprised you can't test it on the ground.

Our procedure is:

Press and hold unfeathering pump.
Should light NTS light.
Engage starter for engine start.
NTS light should go out.
At around 20-30%, NTS light goes back on.

That tests the NTS system by using the negative torque of the starter.

Some airplanes have one light (beta and NTS test combined) like the MU2. Some have separate beta and NTS lights (Commander? Merlin?).

I'd be very surprised if you don't have such a means to test the NTS system.


Have you experienced an engine failure without NTS? Say in a sim?

I think you would take it more seriously if you had.

No NTS test pass, no fly. Scary.

Mike C.

NTS light separate on Commanders, but otherwise follows the MU-2 procedure, pretty much. Comes on, goes off, then comes back on again to finally go out.

Also, the NTS system is not an autofeather system, and to rely on it as such is a trap. You need to identify and take action like on any other twin. But don't take my word for it:

https://www.tc.gc.ca/eng/civilaviation/opssvs/managementservices-referencecentre-2120.html

That's presumptuous. How do you know how I train?


Yes. Usually from 200 ft, or even lower. Have practiced SE go arounds almost to touch down.


I believe I can do them any time I want, so I reject your attempt to cast it as a deficiency in my abilities.

The fact I can continue the approach does not mean pressing on is the safest choice in every situation, however. Flying is about using your judgment to avoid needing your skills. I'm not an airline god like yourself, so I don't need to feel macho and complete the approach, I need to be safe.

In the video posted here, those conditions, had the engine failed at 800 ft, I am going missed and evaluating my options away from the ground. Selecting another airport was a distinct possibility, including going all the way back to KCEF with 4 mile visibility and 2000+ ft ceilings, plus a 12,000 ft runway 300 ft wide. Now that sounds a whole lot safer than an uncertain approach in heavy rain with an engine failure 30 seconds from MDA. That just sounds like the start of a bad accident report to me, and I want to break the chain.


In the checkride, I've never had an engine fail on the glideslope. That's not one of the profiles and they tend to do the profiles just as drawn.

If I did have an engine failure on glideslope in a checkride, and I executed an early go around instead of pressing on, I seriously doubt I would fail. The argument is that I am misconfigured for an SE approach (wrong flaps), so I need to go around while I have altitude to work with, reconfigure for SE approach, and shoot it again. I don't know any DE who would fail that line of action, but maybe you know meaner ones than I do.

I would think it would be more correct to fail me for NOT going around, continuing the approach misconfigured. If I needed to go around, the plane is not in the configuration of the SE approach profile, so I will not get the expected performance.

In any case, pass or fail of the checkride is no measure of what is safe in the real world. I can see how failing a checkride is more important to you as a pro pilot, could be career limiting, but as an owner operator, it isn't a big deal. Do some more training, do the checkride again, no stigma. I've yet to fail a checkride, so I must not be terrible.

I have practiced engine failures on glideslope many times outside of the checkrides. I have executed go arounds or continued depending on circumstances and training goals.

I have experienced, in sim or in airplane training, almost 300 engine failures, about 1 for every 4 flight hours I have in the MU2. An engine failure is a well rehearsed part of my proficiency.

Mike C.

Then you DO have an NTS test. Do it on every engine start. If it fails, DON'T FLY.


Thankfully, no one here claimed it was, so this isn't in dispute.

The NTS system does give the pilot time to be methodical about pulling the correct lever by making the plane far more controllable than without it.

Mike C.

I believe the old SA26AT was the same way. That's what the mechanic said. After the inflight test we flew it to Walnut ridge AR to have the nose gearbox pulled and repaired.

This was 25 years ago, but I just pulled out my manual for it, and can't find any mention of ground testing the NTS... I can't find mention of the NTS at all.. This is a cobbled up manual, sort of like the IIb is a cobbled up airplane.

No, that's on the later models. 680T/V/W's and 681's don't have a NTS test.

I bet there is an SB/STC to add it.

The NTS test requires a pressure sensor on the prop line and a light. The NTS light comes on with prop pressure from the unfeathering pump, goes out when feather valve dumps, comes back on when negative torque is diminished in later part of start.

It is not something that is internal to the engine, so a fairly simple add on.

I'd be nervous about not having a routine NTS test.

Mike C.

Good thing, too, because the factory system it replaced had two sources of pressurization (two engines) and thus it would be less reliable if it didn't have a backup.

Mike C.

In an ACM turbine failure, the bleed air still passes through the 3 heat exchangers built into the ACM system, so the bleed is cooled to some extent, but still hotter than room temperature. An ACM turbine failure does not result in loss of pressurization, just hot air.

On a Citation, same thing since they have the same ACM, except they also have an emergency pressurization system with direct bleed air into cabin. Given they fly in much colder air during cruise, the bleed air isn't perhaps as hot. I know someone who experienced it in a Citation V and it was hot, but not super hot. You can control the temperature somewhat by adjusting engine power.

The Schiff system needs a backup pressurization capability because a failure of the turbo means loss of pressurization, whereas failure of the ACM turbine does not.

Mike C.

Without the backup, it would. That is why there is a backup, to remove that single point of failure that the ACM system it replaced doesn't have.


That's because the ACM heat exchangers are ALWAYS operating on ram air. No door needed, and no door to fail, either. The ACM is always operating the heat exchangers even if the ACM turbine is not operating. There's nothing I can do to STOP the ram air going over the heat exchangers.

Here's the diagram, note the "ambient air in", and "overboard", that's ram air flowing through the ACM heat exchangers. If the plane has airspeed, that air flows even if ACM turbine is frozen. Then the bleed air goes through 3 heat exchangers, precooler, primary, secondary, before being reaching the cabin. This transfers much of the bleed air heat to the outside air.

Mike C.

Mike I think you are wrong.

The ACM you show uses a fan to pull air in. If the fan is not working you have no cooling of the bleed air.

That why RAM AIR is better.

Ram Air definition - air that is forced to enter a moving aperture, such as the air intake of an aircraft.

Dude, you may want to consider how much you can know from a diagram versus reality. I believe Mike knows the reality of this particular system since it's on his plane. He's not wrong in this case.

Yes, there is a small fan attached to the turbine. However, it is only effective on the ground when the aircraft isn't moving much. Once the aircraft starts moving, the scoop that is the opening becomes more dominated by the ram air. Which Mike said, albeit subtly - "if the plane has airspeed...".

You seem to want to vehemently oppose everything Mike says. Not quite sure why. He knows a lot about systems. Perfect? Nah. But... who among us is?

Dude??

I did not post the diagram. Mike posted it to illustrate his point.

That diagram does the opposite it shows a fan in the duct where you tell me RAM air enters.

Should we not question things like that?

I actually agree with Mike on some items, the cirrus jet being just one of them he is also right about the safety credit the chute provides .

I also completely disagree on his idea of a stable approach. An approach ends at 50 HAT or in the flare, not at minimums.

Isn’t that the purpose of BT to exchange ideas.

That's presumptuous. How do you know how I train?


Yes. Usually from 200 ft, or even lower. Have practiced SE go arounds almost to touch down.


I believe I can do them any time I want, so I reject your attempt to cast it as a deficiency in my abilities.

The fact I can continue the approach does not mean pressing on is the safest choice in every situation, however. Flying is about using your judgment to avoid needing your skills. I'm not an airline god like yourself, so I don't need to feel macho and complete the approach, I need to be safe.

In the video posted here, those conditions, had the engine failed at 800 ft, I am going missed and evaluating my options away from the ground. Selecting another airport was a distinct possibility, including going all the way back to KCEF with 4 mile visibility and 2000+ ft ceilings, plus a 12,000 ft runway 300 ft wide. Now that sounds a whole lot safer than an uncertain approach in heavy rain with an engine failure 30 seconds from MDA. That just sounds like the start of a bad accident report to me, and I want to break the chain.


In the checkride, I've never had an engine fail on the glideslope. That's not one of the profiles and they tend to do the profiles just as drawn.

If I did have an engine failure on glideslope in a checkride, and I executed an early go around instead of pressing on, I seriously doubt I would fail. The argument is that I am misconfigured for an SE approach (wrong flaps), so I need to go around while I have altitude to work with, reconfigure for SE approach, and shoot it again. I don't know any DE who would fail that line of action, but maybe you know meaner ones than I do.

I would think it would be more correct to fail me for NOT going around, continuing the approach misconfigured. If I needed to go around, the plane is not in the configuration of the SE approach profile, so I will not get the expected performance.

In any case, pass or fail of the checkride is no measure of what is safe in the real world. I can see how failing a checkride is more important to you as a pro pilot, could be career limiting, but as an owner operator, it isn't a big deal. Do some more training, do the checkride again, no stigma. I've yet to fail a checkride, so I must not be terrible.

I have practiced engine failures on glideslope many times outside of the checkrides. I have executed go arounds or continued depending on circumstances and training goals.

I have experienced, in sim or in airplane training, almost 300 engine failures, about 1 for every 4 flight hours I have in the MU2. An engine failure is a well rehearsed part of my proficiency.

Mike C.

Only there for ground ops. The scoops on the airplane make it redundant with airspeed. It is one of the reasons the ACM is not as effective on the ground as in the air, less ambient air flow.

Mike C.