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Engine Auto-Deceleration in Reverse Based on Groundspeed

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Engine Auto-Deceleration in Reverse Based on Groundspeed

Old 20th Apr 2021, 13:46
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Engine Auto-Deceleration in Reverse Based on Groundspeed

Looks like the Citation Longitude has a FADEC controlled feature where the engines automatically decelerate to a 'safe level' regardless of thrust Lever position as the aircraft slows. Has anybody seen this feature on any other aircraft and is there a name for this feature.
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Old 20th Apr 2021, 15:36
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N1 mini?


I’ll get my coat
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Old 20th Apr 2021, 19:46
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Sounds like N1 mini Or another name for Approach Idle?
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Old 21st Apr 2021, 01:25
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The Global 5000 has a similar feature. From the FCOM:

”The EEC modulates engine power with maximum reverse thrust selected. A maximum of 70% N1 is available above 65 knots. Engine power is linearly reduced to a maximum of 50% N1 at 50 knots and below.”

It doesn’t say whether it’s ground speed or airspeed. Probably ground speed. There is no name given for this feature.
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Old 21st Apr 2021, 06:59
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Ah. Perhaps Bombardier should trademark the name "N1 maxi".

Getting my hat...
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Old 21st Apr 2021, 09:07
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Similar on the A220, they call it thrust reverse auto cutback, reducing thrust to reverse idle once below 60 kt.
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Old 21st Apr 2021, 09:41
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Is it just me who thinks that engine life should come second to safety when it comes to stopping on a contaminated runway, where full reverse thrust could be required even at low speeds?
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Old 21st Apr 2021, 13:25
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No, it's not just you. It saved my bacon in a 727 at KLGA circa 1980.
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Old 21st Apr 2021, 17:22
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FlyingStone

True! They could have an override mechanism for emergency.
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Old 21st Apr 2021, 17:32
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Or just keep it simple, and train pilots to select idle reverse at 60kts (if conditions allow), like on... any other airplane?
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Old 21st Apr 2021, 18:29
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aterpster

Given the conditions then, would the approach and landing be legal under today's rules, under TALPA-ARC and OLD landing performance concepts? I.e. did we grow wiser about what shall not even be attempted - at least on paper? An honest question. Hoping for a positive answer while a negative one will have more educative value. Thanks.
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Old 21st Apr 2021, 18:33
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vilas

What could go wrong with that ...
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Old 21st Apr 2021, 20:45
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FlightDetent

Some years ago at East Midlands the snow had been cleared and Braking action reported as good. We were the first to land and had to go to the end to vacate. All well until the last 1500 ft which was sheet ice and all 8 "R" lights on the anti skid panel were going on-off-on-off. We were doing about 40 knots and the reversers were all that saved us from going off the end.
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Old 22nd Apr 2021, 00:20
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Originally Posted by FLX/MCT View Post
Similar on the A220, they call it thrust reverse auto cutback, reducing thrust to reverse idle once below 60 kt.
I guess the A220 isn’t fitted with ROPS. MAX BRAKE ... MAX REVERSE. Aye Captain, she won’t give no more.
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Old 22nd Apr 2021, 01:02
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Originally Posted by Flying Stone
Is it just me who thinks that engine life should come second to safety when it comes to stopping on a contaminated runway, where full reverse thrust could be required even at low speeds?
Virgin Australia found the benefit to max reverse down to 20 kts in a737 a few years ago when landing on a wet runway, stopping just 5m from the departure end. The ATSB report.

To my mind, if you need to bend, or break, parts of the airplane to prevent a greater incident, you should be able to. If that means full reverse down to 0kts so be it. Too many of my toys at work (another industry, not flying anymore) have these self-protection features and they work well 99.9% of the time. The other .1% they increase the hazards or introduce additional safety risks.
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Old 22nd Apr 2021, 03:16
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Hopefully if the plane goes off a cliff at the end of the runway, the engine won’t be damaged too badly...

Any engineering types tdracer care to comment on what failure modes the manufacturer would have considered before implementing this feature?
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Old 22nd Apr 2021, 05:41
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I don't know the details, but could it be to prevent/reduce damage to turbine blades like on the F100?
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Old 22nd Apr 2021, 05:54
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I understand why they'd want it, my question was about what things they'd have considered as possible failure points before designing the plane this way. Seems like a solution to a problem that doesn't exist. If anything, people come out of reverse prematurely, not too late.

As has been mentioned before, it seems any point of failure in this system will potentially cost way more than a pair of engines.
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Old 22nd Apr 2021, 08:12
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1. Trying to prevent fod ingestion
2. engine instability due possible reingestion of burnt exhaust gases(reverser looks to be both core and fan reverse)

that’s my best guess. Id assume driver couldn’t give a rodents bum about either if he is running out of pavement.

not sure why they did it on the 220 as it’s a fan reverser. Maybe it will get binned when they figure how to install ROW/ROPS.
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Old 22nd Apr 2021, 08:34
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Maybe one answer is to use a bigger safety factor when landing on contaminated runways in this type? It seems strange that there is no mention of an override: at least with most implementations of thrust levers, if you push them as far forward as they go, you get the most the engine can produce, even if you’re using reduced thrust at the time. If you yanked the reversers back all the way, you’d hope the system would recognise that was what you wanted, irrespective of everything else. Like “ground contact imminent” when airborne.

I too have had a pucker-factor 50 moment landing on a slushy runway and having to rely on full reverse to bring us to a halt ~50m short of the end, due to the braking action being very different from that reported. We might have made it going to idle but it wasn’t research I wished to conduct at the time...
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