Testing of idle reverse thrust before takeoff. A wise precaution?

[A37575]

https://avherald.com/h?article=4c5b3f3d&opt=0

An A320 lands and reverse thrust fails to operate. There had been no prior warning flags in the cockpit. Maintenance staff had forgotten to remove the reverser lockout pins after servicing. The situation could have been critical if a high speed rejected takeoff occurred at the departure airfield and the crew were unaware the reversers had been locked out.

System caution lights have removed the once good airmanship requirement of the momentary testing of brakes after moving from the tarmac. However, the above incident illustrates that on this occasion a fault in reverser operation did not show up to the cockpit crew until too late

A short test of reverse idle at an appropriate point before takeoff would have revealed this maintenance defect.. Another cue for good airmanship?
.

[Stan Woolley]

A short test of reverse idle at an appropriate point before takeoff would have revealed this maintenance defect.. Another cue for good airmanship?
.

Not for me thanks. A reverser not working is rarely that big a deal on landing, but messing with reversers before take off just doesn’t give me a good vibe!

[Uplinker]

https://avherald.com/h?article=4c5b3f3d&opt=0

An A320 lands and reverse thrust fails to operate. There had been no prior warning flags in the cockpit. Which is one reason why PM calls reversers green/amber during rollout.

..........and the crew were unaware the reversers had been locked out.

I think the reverser lockout pins are visible on the sides of the engine nacelle, when fitted?

......... Another cue for good airmanship? Or checking during the walkaround to see if the lockout pins had been fitted?

[A37575]

A reverser not working is rarely that big a deal on landing
But could be a seriously big deal on a high speed rejected take off if runway limited..

[lomapaseo]

A thought

The plane is certified to stop safely with the reversers locked out.

Give a thought to how many tasks you want to perform over and above what's in the manuals

[Stan Woolley]

But could be a seriously big deal on a high speed rejected take off if runway limited..

As lomapaseo has said, even in that case a failure should not be too critical. And how often are we really runway limited on take off? Going full power/ full length.
I’m with the previous poster. Why make things more complicated? KISS. YMMV

[sonicbum]

A short test of reverse idle at an appropriate point before takeoff would have revealed this maintenance defect.. Another cue for good airmanship?
.

Just in case I would also check the spoilers movement, and check the engines are getting up to toga thrust should I need it, and also check the flaps travel down to 3 if I need to come back quickly and also I would close manually the outflow vale and pressurise the plane to check it does pressurise. Anyway short answer to the above : no, it's not, as performance data is there for you to consider a no reverse situation up to a contaminated runway.

[FullWings]

I agree with most of the posters here: it’s not a major issue 99.99% of the time should they not deploy, plus static use of of thrust reversers is not helpful in terms of FOD and/or surging. After all, if you’re going to check they work properly that involves full reverse...

[josephfeatherweight]

Many aircraft require a pre-take-off reverser check as part of the taxi checklist.

[atakacs]

Many aircraft require a pre-take-off reverser check as part of the taxi checklist.
Any specifics ?

[Meikleour]

Forty+ years ago on the B707-436 with R-R Conway engines reverse was indeed checked on taxy out. Try that with a JT3D powered aircraft and you will be in a whole world of pain!

[FlightDetent]

But could be a seriously big deal on a high speed rejected take off if runway limited.. On dry runways the effect of REV is not taken into account for PERF calculations. The scenario you fear is (all need to apply at the same time)
- wet runway or worse
- ASDA limited take-off
- RTO at V+-10 to V1

The chances are very remote. For what is left, the standard walk around check of REV lock-out pins should cover. No need to envisage new procedures where at least 50% compliance with the present ones would do. Agreed?

-----

although from the report: https://www.atsb.gov.au/media/5775766/ao-2018-064_final.pdf
it is not clear whether the standard pin as seen here https://www.atsb.gov.au/media/5775766/ao-2018-064_final.pdf was visible on the outside of the casing.

Now, the paragraph "AMM specific wording of HMU deactivated ..." of the report is the funny part.

[metro301]

https://avherald.com/h?article=4c5b3f3d&opt=0
An A320 lands and reverse thrust fails to operate. There had been no prior warning flags in the cockpit. Maintenance staff had forgotten to remove the reverser lockout pins after servicing. The situation could have been critical if a high speed rejected takeoff occurred at the departure airfield and the crew were unaware the reversers had been locked out.

Highly visible lock out pins should have been caught on even the most cursery walkaround.

[QuarterInchSocket]

The HCU is under the pylon on left side underneath the cowling, it isn't visible externally so can't detect incorrect HCU config during walk-around.

There is a streamer-free pin that lives up there and stays with the aircraft. that is what the engineers used to lock out the reversers and forgot to remove.

Very sloppy maintenance. If I'm not mistaken, landing performance is predicated on braking action with nil reverser credit? (I'm not a pilot).

[sonicbum]

Very sloppy maintenance. If I'm not mistaken, landing performance is predicated on braking action with nil reverser credit? (I'm not a pilot).

Correct. The only difference is that, in case of landing on a contaminated runway, You need to take it into account from a performance point of view (i.e. add the impact of a no reverser configuration).

[QuarterInchSocket]

Thanks sonicbum. I forgot to ask. Would the takeoff run be the same?

[ScepticalOptomist]

I agree with the ‘not a good idea’ crowd.

Also on every Boeing I’ve flown selecting REV on the ground deletes all your Vspeeds from the FMC.

Keep It Simple, just follow manufacturer and company SOPs.

The willingness not to, as alluded to by some of the questions on this forum, do make me worry about my fellow aviators.

[PPRuNeUser0215]

Any specifics ?

Global Express, Citations, I suspect Gulfstreams too. Never seen in done on modern airliners though

[Escape Path]

A proper walk around/cockpit preparation goes a long way to prevent stuff like this... Should’ve spotted the reverse lockout pins and all this discussion would be inexistent.

As sonicbum said, might as well check everything every time, just in case.

Reverse is not credited for RTO in dry runways, it is credited for wet or contaminated runways though

[stilton]

Forty+ years ago on the B707-436 with R-R Conway engines reverse was indeed checked on taxy out. Try that with a JT3D powered aircraft and you will be in a whole world of pain!


Ok, I’ll bite, why is that ?

[vilas]

Never tired of saying don't make your own procedures. If too tempted ask the manufacturer. This becomes an addiction. And on aircraft run on software can have other effects which are not obvious.

[Australopithecus]

What a good idea! I might check the gear operation too in case those pins were left in.

Don't invent procedures, don't deviate from the FCOM. At least not without good, compelling reason to do so. A misplaced sense of caution does not satisfy that condition. And my sarcasm aside, where do you stop? Eventually you'll be cycling every switch and doing a compass swing.

[rog747]

707-436 RR Conway testing R/T before TO v JT3D engines

Ok, I’ll bite, why is that ?


I was not aware of that on the BOAC RR 707's, but if you open the reversers on a PW JT3D they have fan cold and hot end sliding cowls, and very often one would not fully close up after landing.
The RR engine on the 707 had cascade type reverser built by RR
(the DC8 43 Conway application was different with a Douglas transiting ring thrust reversers and exhaust silencers)

[VinRouge]

But could be a seriously big deal on a high speed rejected take off if runway limited..

Reject executed at V1 will only give you a 50% chance of stopping in the remaining distance anyway with a critical propulsive loss at engine failure recognition speed with a balanced field.

Its calculated using Gross not
Net data.as others say, do a proper walk around. All you will do by cycling each and every flight is put extra wear on components and increase the likelihood it won’t work when you need it most.

[john_tullamarine]

Reject executed at V1 will only give you a 50% chance of stopping in the remaining distance anyway

Its calculated using Gross not Net data.

You wouldn't like to expand on these points, would you ?

[tdracer]

Thrust reversers fail to deploy for a number of reasons - the numbers are better now than they used to be, but figure roughly once in every 5,000 to 10,000 deployments a T/R will fail to properly deploy due to some fault, and someone forgetting to remover the lockout pins is pretty low on the probability list of failures.
As VinRouge notes, deploying the T/R prior to every takeoff just wears them out quicker, and makes it a little more likely one will fail when you really need it.
Besides, what are you going to do if one fails to deploy on a pre-takeoff check? Most likely you're go to go back, take a delay while the T/R gets deactivated and locked out, then depart with a reverser that doesn't work - which is what you're would have done anyway except now you're doing it several hours later...

[Tom Sawyer]

Checking reversers with the aircraft stationary at the end of the runway or on the taxiway not a good idea as the reversed exhaust gas flow could blow stones or any other FOD up which could get ingested into the fan or core and cause you an even more significant problem. Not sure what flight crew operating procedures say about stowing reversers on landing at what speed to prevent this (and I'm pretty sure you don't use T/Rev to come to a complete stop), but as an Engineer we do not usually carry out an engine running reverser check on ramp for this reason. We usually have a facility through the CMS to do a cycling check using electrics or hydraulics. I can only speak for what I work on (Airbuses and B744), and there could be exceptions to this.......and yes I do know cascade vanes are designed to mitigate the ingestion of blown up FOD, but still good practice I'm sure.

[Atlas Shrugged]

But could be a seriously big deal on a high speed rejected take off if runway limited..

Not really......

A37575, you have to remember that there is very little, if any, reverse thrust. Most reversers only affect the fan air, not the flow from the core. Whilst the fan flow might generate some reverse, the core is still pushing you along. All reverse really does in an airliner is cancel out the core thrust, and not much more. It does destroy the lift generated by the wings and may dissipate any water that might be on the runway - both help sit the aircraft down on the ground a bit more firmly - but that's about it.

[Smythe]

Well, the ground crew will love you, after they finish picking everything up.

[stilton]

I was not aware of that on the BOAC RR 707's, but if you open the reversers on a PW JT3D they have fan cold and hot end sliding cowls, and very often one would not fully close up after landing.
The RR engine on the 707 had cascade type reverser built by RR
(the DC8 43 Conway application was different with a Douglas transiting ring thrust reversers and exhaust silencers)


Interesting, thanks for that !

[Centaurus]

All reverse really does in an airliner is cancel out the core thrust, and not much more. It does destroy the lift generated by the wings and may dissipate any water that might be on the runway - both help sit the aircraft down on the ground a bit more firmly - but that's about it.
https://www.pprune.org/images/statusicon/user_offline.gif https://www.pprune.org/images/buttons/report.gif (https://www.pprune.org/report.php?p=10428890)
The above argument would suggest having a reverse thrust system at all is a very expensive exercise in poor cost effectiveness. Why haven't the manufacturers realized this and built their aircraft without reverse thrust? Save millions of $$$ in maintenance costs. OK - reverse might be handy on slippery runways when wheel braking efficiency is reduced but it could be cost effective to accept that risk.:ok:

[DaveReidUK]

A37575, you have to remember that there is very little, if any, reverse thrust. Most reversers only affect the fan air, not the flow from the core. Whilst the fan flow might generate some reverse, the core is still pushing you along.

Almost all of the thrust generated by a large turbofan comes from the fan, so it's illogical to suggest that the absence of a core reverser makes much difference.

Early RB211s, for example, had both but the core reverser was subsequently deleted because it was a PITA for very little benefit.

[mustafagander]

Centaurus,
Look at the A380 - only reversers on #2 & #3. Just enough to claim the "major means of deceleration" for certification but really a WOFTAM.
The concept of testing reverse thrust prior to each takeoff is simply risible - where do you stop testing? Reversers and brakes worked fine last landing or there would be a tech log entry so just fly the aircraft FFS and not try to do block overhaul each T/R.

[Tom Sawyer]

The above argument would suggest having a reverse thrust system at all is a very expensive exercise in poor cost effectiveness. Why haven't the manufacturers realized this and built their aircraft without reverse thrust? Save millions of $$$ in maintenance costs. OK - reverse might be handy on slippery runways when wheel braking efficiency is reduced but it could be cost effective to accept that risk.:ok:

Not sure if this true or not but heard it few times now......the A380 was originally designed with no T/Rev, but it was the regulators who said that it had to have it as the design spec for that standard of aircraft dictated it and so it was installed on the inboards to satisfy them.

[Tom Sawyer]

Not really......

A37575, you have to remember that there is very little, if any, reverse thrust. Most reversers only affect the fan air, not the flow from the core. Whilst the fan flow might generate some reverse, the core is still pushing you along. All reverse really does in an airliner is cancel out the core thrust, and not much more. It does destroy the lift generated by the wings and may dissipate any water that might be on the runway - both help sit the aircraft down on the ground a bit more firmly - but that's about it.

80% of a modern, high by-pass engine's thrust comes from the fan. The core engine is really only there to drive the fan, the gearboxes for the ancillary pumps/generators etc. , and provide bleed air for air conditioning/anti-icing. On that basis Fan T/Rev thrust significantly cancels out Core Thrust during application of of T/Rev.

[lomapaseo]

The above argument would suggest having a reverse thrust system at all is a very expensive exercise in poor cost effectiveness. Why haven't the manufacturers realized this and built their aircraft without reverse thrust? Save millions of $$$ in maintenance costs. OK - reverse might be handy on slippery runways when wheel braking efficiency is reduced but it could be cost effective to accept that risk.:ok:

All true and revisited years ago in regulatory discussions.

In the end there was a realization that there was a money making business to offer the pilots what they wanted

[CV880]

Re post #34, Airbus once proposed at one of the A3XX airline working groups back in the 1990's to delete all thrust reversers to save weight and complexity however the airline working group recommended at least 2 engines have reversers. The main reason for rejecting the no reverser proposal was the estimated required runway length at MTOW for a slippery/contaminated runway if I recall correctly..

[Chu Chu]

A reverser test after maintenance seems to makes sense -- by someone at least. One of the major missteps in the the report was that the engineers skipped a required functional test. Of course, that doesn't mean that the flight crew should repeat it just in case . . .

[Atlas Shrugged]

On that basis Fan T/Rev thrust significantly cancels out Core Thrust during application of of T/Rev.
I know....

[stilton]

The above argument would suggest having a reverse thrust system at all is a very expensive exercise in poor cost effectiveness. Why haven't the manufacturers realized this and built their aircraft without reverse thrust? Save millions of $$$ in maintenance costs. OK - reverse might be handy on slippery runways when wheel braking efficiency is reduced but it could be cost effective to accept that risk.:ok:


Those savings will be gone pretty quickly
after you slide off the end of the runway in
dodgy braking conditions and bend your kite


Reverse is invaluable in those conditions, I’ll take all the deceleration devices there are, sometimes you need all of them

[lomapaseo]

Reverse is invaluable in those conditions, I’ll take all the deceleration devices there are, sometimes you need all of them

Keep it simple add a drag chute for the few times you need it

[memopilot]

I think the only acceptable test of reverses before takeoff in the A320 is if OAT is below -40°C

Regards !

[fokkerjet]

Global Express, Citations, I suspect Gulfstreams too. Never seen in done on modern airliners though

to add...Gulfstreams, Fokkers and Falcons. I recall it was all the rage to pull back from the gate using reverse thrust..so DC9s (all series) for sure and maybe B727s. On biz jets, we tend to use idle reverse to control taxi speed since most jets will continue to accelerate (to a point, of course) at idle.

[propnut]

No reversers at all on F28s. Added to F100s

[tdracer]

Not really......

A37575, you have to remember that there is very little, if any, reverse thrust. Most reversers only affect the fan air, not the flow from the core. Whilst the fan flow might generate some reverse, the core is still pushing you along. All reverse really does in an airliner is cancel out the core thrust, and not much more. It does destroy the lift generated by the wings and may dissipate any water that might be on the runway - both help sit the aircraft down on the ground a bit more firmly - but that's about it.

A lot of mis-information floating around on this thread, such as the above :rolleyes:
Most thrust reversers do create a significant amount of net reverse thrust, particularly at higher airspeed (i.e. over ~100 knots) due to the ram drag of all that fan air going into the inlet. While it's true the core thrust cancels some of the reverse fan thrust, it comes no where near cancelling all the reverse thrust (it is why you'll note that max reverse N1 is typically fairly low - in the 80-85% N1 range - above that the reverse fan thrust doesn't increase as fast as the core forward thrust so a higher N1 doesn't stop you any quicker.)
Even statically, there is enough reverse thrust that you can power back a 767/CF6-80C2 (been there, done that - during flight testing). Obviously not an approved procedure though - very, very hard on the engines due to all the re-ingestion.

During the development phase of the 777, I ask the question - part in jest but also part seriously - why don't we just get rid of the reversers. They're heavy, maintenance intensive, and a T/R malfunction was blamed for the recent Lauda 767 crash. I was told the use of reverse reduces brake wear so much it saved between $50 and $100 on every landing...

[mustafagander]

tdracer,
How come then many airlines SOP is idle reverse and use the brakes to stop?
We were told the opposite - reverse costs way more than brakes due temp cycles and fuel burn. We plebs flying the beast have no idea, it's their train set so we play with it their way.

[DaveReidUK]

I was told the use of reverse reduces brake wear so much it saved between $50 and $100 on every landing...

How come then many airlines SOP is idle reverse and use the brakes to stop?

Those two statements are not mutually exclusive. Any use of reverse, even at idle, will reduce brake wear.

[sonicbum]

The always green dilemma reverse thrust / brake wear / landing CONF does not come with a one size fits all solution. It is very much dependant on the Operator's types of operations (legacy, low cost, charter, short-medium-long haul etc..) and the related cost analysis.

[Stan Woolley]

tdracer,
How come then many airlines SOP is idle reverse and use the brakes to stop?
We were told the opposite - reverse costs way more than brakes due temp cycles and fuel burn. We plebs flying the beast have no idea, it's their train set so we play with it their way.

During the development phase of the 777, I ask the question - part in jest but also part seriously - why don't we just get rid of the reversers. They're heavy, maintenance intensive, and a T/R malfunction was blamed for the recent Lauda 767 crash. I was told the use of reverse reduces brake wear so much it saved between $50 and $100 on every landing..

I joined Ryanair in 2005 and was surprised that their SOP was to use full reverse after coming from a few operators that had used idle reverse for a long time before. So that might imply that they for one believed reverse (and autobrake)was the better option to save money. As you say, we just comply.

tdracer
I remember reading a really interesting response to a thread by a man (I’m sure his surname was Green) on an aviation forum in the nineties. The conversation was about how best to deal with a reverser deploying after take off, as it’s a possible failure in the simulator. He had been( maybe still was) a Boeing test pilot. He gave me the impression that unless you were very very lucky, this was one failure that would end in a crash. I seem to remember him saying that they’d investigated the 737-400 and saying that the results of a failure of a reverser on that variant was pretty frightening. It of course had the sleeve type reverser, rather than the bucket type on the -200, which was even worse. :eek:

edit: He said that to have any chance you’d have to get the engine shut down very quickly, as well as getting above a certain speed (V2 + ?).

[RetiredBA/BY]

Perhaps it has been mentioned but selecting reverse idle during taxi, say, as I did once, to help keep brake temps down, dumps the derates on the AT.

Do that on the 75/76 and selecting TOGA gives you full thrust for takeoff if you forget to reselect D 1 or D2, fantastic acceleration on a light aircraft though !

Reversers were checked on Concorde during taxi out.

[Centaurus]

Call it overkill but after reading about a fatal accident where the leading edge devices for some reason failed to extend during the before takeoff checks, I must admit to always after that, looking through my side window to confirm the LED's on my side were indeed extended in the 737-200. Strangely enough I didn't ask the occupant of the other seat to check his side. But it gave me peace of mind if nothing else. The use of idle reverse on the ground in the 737-200 was frequently "cracked" to keep taxi speed within commonsense limits.without having to ride the brakes so at least we knew they worked before take off. These little quirks were considered good airmanship by some and and superfluous nonsense to others.

[742]

tdracer,
How come then many airlines SOP is idle reverse and use the brakes to stop?
We were told the opposite - reverse costs way more than brakes due temp cycles and fuel burn. We plebs flying the beast have no idea, it's their train set so we play with it their way.

At my operator "idle reverse only" came out of a check airman meeting in which both GE and Goodrich representatives spoke. GE presented that reverse was the greatest evil civilization has ever faced, while Goodrich didn't care if the airline used reverse or not. Apparently no one considered that the engines were leased/under maintenance contract while the brakes were simply purchased as needed, thus the interests of the two suppliers were very different.

I do know for certain that no one considered the amount of landing performance work actually done on contaminated runways during certification.

It has always fascinated me how individual departments in an airline can use very sharp pencils, but when it comes to pulling it all together it is more crayons and markers.

[SeenItAll]

I joined Ryanair in 2005 and was surprised that their SOP was to use full reverse after coming from a few operators that had used idle reverse for a long time before. So that might imply that they for one believed reverse (and autobrake)was the better option to save money. As you say, we just comply.
Is it possible that Ryanair's (an LCC that does quick turns) reason for using full reverse was because it would reduce brake heat-up and the cooling interval that would need to pass before the next takeoff?

[tdracer]

tdracer
I remember reading a really interesting response to a thread by a man (I’m sure his surname was Green) on an aviation forum in the nineties. The conversation was about how best to deal with a reverser deploying after take off, as it’s a possible failure in the simulator. He had been( maybe still was) a Boeing test pilot. He gave me the impression that unless you were very very lucky, this was one failure that would end in a crash. I seem to remember him saying that they’d investigated the 737-400 and saying that the results of a failure of a reverser on that variant was pretty frightening. It of course had the sleeve type reverser, rather than the bucket type on the -200, which was even worse. :eek:

edit: He said that to have any chance you’d have to get the engine shut down very quickly, as well as getting above a certain speed (V2 + ?).

I was directly involved in the Lauda 767 investigation - probably the hardest, most unpleasant thing I ever did at Boeing. During the investigation, they were (coincidentally) running some 777 developmental thrust reverser efflux testing at the Boeing Vertol facility in Philly (useful as it had a moving ground plane capability). Well the wing/engine layout of the 777 is very similar to the 767 - just scaled up - so after the wrapped up the 777 testing, we went in and did some testing. It was a 'half model' - so a single engine with a wing and half fuselage - the 'engine' used a 'Turbine Powered Simulator' or TPS - high pressure air piped in through the wing and strut ran a turbine the drove a 'fan', while the TPS exhaust became the core exhaust. It was a good sized model - 1/10th scale IIRC. We removed the ground plane, changed the wing to a clean, flaps up configuration, and did a bunch of testing measuring the lift, drag, and controllability characteristics. It was almost funny - there was an Aero S&C guy there also witnessing the testing that swore up and down that the Lauda pilots had screwed up - that the deployed T/R was fully controllable - until we started testing. As the testing progressed, and he reviewed the data, he got really quiet. Being a propulsion guy, I didn't really understand all those control coefficients (I'd taken some Aero S&C classes in college, but that had been over 15 years earlier and I didn't recall much of it). But the last test we did was a flow visualization - they taped hundreds of yarn tufts on the upper surface of the wing and tail - and it was stunning. Nearly the entire upper surface of the wing was separated, as was most of the tail (both horizontal and vertical).

Ultimately it was determined that it simply was not practical to make an in-flight deployment controllable with the (then new) very high bypass turbofan engines, the only answer was to make sure it never happened. Hence the retrofit of the 'third lock' (aka 'sync lock', although not all installations use an actual lock on the sync cable).

[Stan Woolley]

Ultimately it was determined that it simply was not practical to make an in-flight deployment controllable with the (then new) very high bypass turbofan engines, the only answer was to make sure it never happened. Hence the retrofit of the 'third lock' (aka 'sync lock', although not all installations use an actual lock on the sync cable).

Thanks again, very interesting.
You’ve reminded me, this was another point made by Green, trying to make sure it never happened.

[island_airphoto]

The always green dilemma reverse thrust / brake wear / landing CONF does not come with a one size fits all solution. It is very much dependant on the Operator's types of operations (legacy, low cost, charter, short-medium-long haul etc..) and the related cost analysis.

When I flew a C-208 we seemed to change between brakes and reverse weekly :rolleyes: You guys are wearing out the brakes! You guys are putting nicks in the prop!

[Smythe]

We were being told to reduce thruster use, as the cycles count towards engine overhaul...much cheaper to replace brakes than an engine.

[DaveReidUK]

We were being told to reduce thruster use, as the cycles count towards engine overhaul...much cheaper to replace brakes than an engine.

Out of interest, do you know if application of reverse idle (the subject of the thread) counted as an additional engine cycle ?

[lomapaseo]

Out of interest, do you know if application of reverse idle (the subject of the thread) counted as an additional engine cycle ?

Very doubtful

In general engines care about EGT (time at) and RPM magnitude. The RPM equates to cyclic fatigue of the metal in the rotor-disks. This cyclic life equates mostly to the average flight max RPM (with a goodly amount of margin). So if the RPM in reverse approaches typical takeoff, then it probably counts towards fatigue life of some rotor parts

[LeadSled]

tdracer,
How come then many airlines SOP is idle reverse and use the brakes to stop?
We were told the opposite - reverse costs way more than brakes due temp cycles and fuel burn. We plebs flying the beast have no idea, it's their train set so we play with it their way.
Folks,
Whether the aircraft has carbon or steel brakes makes a significant difference in costs estimates per landing.
In my experience it favours using reverse with steel brakes, and idle reverse only for carbon brakes.
As many of you will know, carbon brakes do not like being used "gently" ---- the wear rate is much higher cold than at "normal" working temperature, the reverse of steel brakes
Tootle pip!!

[LeadSled]

I was directly involved in the Lauda 767 investigation - probably the hardest, most unpleasant thing I ever did at Boeing.
snip
Ultimately it was determined that it simply was not practical to make an in-flight deployment controllable with the (then new) very high bypass turbofan engines, the only answer was to make sure it never happened. Hence the retrofit of the 'third lock' (aka 'sync lock', although not all installations use an actual lock on the sync cable).

A very good friend of mine flew that Lauda B767 into Bangkok on its previous sector.
I was flying B767 with P7W JT9D-7RE at the time.
It is a long time ago, and almost as long since I read the report, but all I can say is we introduced company changes to "SOP" within 48 hours of the accident.
Stick to the AFM for the aircraft, do not invent additional procedures --- and any change must be approved by the Type Certificate holder and the state of certification.---- all done in that 48 hours, in our case.
Tootle pip!!

[Mach E Avelli]

‘Stuff’ that must be tested will be listed in the FCOM and AFM.
Otherwise leave it alone!. It could be argued that the more often something is cycled, the closer you bring it to failure. Landing lights come to mind. If they worked OK last night, chances are they will work tonight without you flicking them on and off, ‘just to check’ (and after the engineers probably already checked).
But of course if your anal SOP says to do it, you do it.

[six string]

In our OPT iPad, the reversers make a significant difference to landing distances in two engine operative as well as single engine landings, and wet runways as well. It either makes that real difference or they’re telling big porkies! Our SOPs state, do not stow reversers until stopping is assured. I can feel the difference. An aside, I can feel the difference in stowing the speed brakes as well.

but I do not check them taxiing out.

A few few times I’ve left them out a bit longer than normal, and a few times had the reverser light on the overhead illuminate, so I put them away in good time when decreasing below 80 knots +/-