Very impressive, so much so, I ran the numbers for the S21 example on wet snow, aka slush.

S21 is 4164 ft elevation, 5460 ft long.

Taking 75% of that is 4095 ft. Going to the contaminated takeoff chart, flaps 15, for 0.125 slush, that translates to a dry runway requirement of 1865 feet.

Looking at flaps 15 takeoff charts for dry runway, 0 C (assuming slush temperature), 4000 ft elevation, anti ice off, there is no weight which will yield a dry runway distance of 1865 ft. At a very light 6000 lbs, the distance is 2480 ft, so you are well over the requirement.

As I read the charts, there is no way you can operate at S21 with 0.125 slush and meet book numbers, even at 100% runway length.

Did I miss something?

For my Citation V, S21, 0 C, 15,900 lbs (max), dry runway length is 3460 ft.

If the runway is covered in ice my takeoff length using TRs is 5281 ft, and thus works. If I reduce weight to Mustang cabin load and range, that is, same mission, my numbers would get better.

Again, this was on *ICE*, the worst case condition. Wet, standing water, slush, snow are all less than that.

I don't see how you can say TRs don't add capability, the numbers say otherwise. If we both wake up some slushy morning and head out to S21, I can leave and you can't.

Mike C.

Yes. We did TR emergencies about 6 times in the sim. Not terribly difficult to deal with if properly trained.

My take away was this: if ANY TR light illuminates OR you suspect any issue with a TR, hit BOTH EMER STOW switches. No short term penalty to do that, then sort it out with altitude.

A TR deployed is way less critical than feathering a prop on a twin. The TR system automatically pulls the power lever back if it opens which helps reduce the issue quite a bit.


I don't know if the sim profile is based on models or measurements or perhaps a mixture of both.

I'd surmise it was actually tested in the air for certification, though it doesn't have to be at very low altitude.

AC 25-7D, Flight Test Guide for Part 25, says this:

"For reversers intended to be operable on the ground only, it must be shown that the airplane can be safely landed and stopped with a critical engine reverser deployed. In addition, if an undamaged reverser inadvertently becomes deployed in flight, it must be shown that it can be safely restored to a forward power or thrust position."

Since this is the flight test guide, one presumes this is in flight. Of course, this is the current revision of the flight test guide, it might have been different back in the day.

Mike C.

Yes. We did TR emergencies about 6 times in the sim. Not terribly difficult to deal with if properly trained.

My take away was this: if ANY TR light illuminates OR you suspect any issue with a TR, hit BOTH EMER STOW switches. No short term penalty to do that, then sort it out with altitude.

A TR deployed is way less critical than feathering a prop on a twin. The TR system automatically pulls the power lever back if it opens which helps reduce the issue quite a bit.


I don't know if the sim profile is based on models or measurements or perhaps a mixture of both.

I'd surmise it was actually tested in the air for certification, though it doesn't have to be at very low altitude.

AC 25-7D, Flight Test Guide for Part 25, says this:

"For reversers intended to be operable on the ground only, it must be shown that the airplane can be safely landed and stopped with a critical engine reverser deployed. In addition, if an undamaged reverser inadvertently becomes deployed in flight, it must be shown that it can be safely restored to a forward power or thrust position."

Since this is the flight test guide, one presumes this is in flight. Of course, this is the current revision of the flight test guide, it might have been different back in the day.

Mike C.

No, it doesn't, the presumption is that the bucket gets stowed quickly and you can then fly away with two engines so your performance profile then greatly exceeds the OEI profile that you based your departure on.

If you are fast, the reverser might stay out even in EMER STOW due to bucket drag. But you have speed, and thus you can hold altitude or even climb while you deal with the deployment.

If you are slow, then EMER STOW will pull the reverser in fairly quickly, so the performance penalty will be transitory. At slow speed, the drag will also be less for the extended bucket.

My manual says to stay below 125 KIAS until the reverser stows, so that speed has to be slow enough to allow that to happen. Once stowed, do not exceed 200 KIAS and you can use both engines. Then you should land and have the failure addressed.

If the reverser won't stow, the EMER STOW system has failed, then you shut down that engine, maintain 150 KIAS or slower, and land. You can control the airplane with a reverser out. This would be a double failure (inadvertent deployment followed by a failed EMER STOW system), which should be rare, and this will likely not meet the OEI gradients. At this point, you may have to be creative. It is not clear this has ever occurred in Citation operational history.

As for sim modeling, I presume this was modeled using PWC data. Unless one instruments a plane and tries it, the model is all you got. Much of the sim is like that, I suspect.

There are very few TR related accidents in the Citation record, so it seems to work reasonably well.

Mike C.

The numbers I ran were for landing distances.