Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
TC957
Topic Author
Posts: 4172
Joined: Wed May 23, 2012 1:12 pm

Biz-jet thrust reversers activated whilst taxiing.

Sat Jul 10, 2021 9:23 pm

Why do biz-jets, especially Gulfstreams and Globals, deploy their thrust reversers whilst taxiing out ? And in sometimes too.
It's that you don't see airliners doing this.
Thanks.
 
User avatar
fr8mech
Posts: 8382
Joined: Mon Sep 26, 2005 9:00 am

Re: Biz-jet thrust reversers activated whilst taxiing.

Sat Jul 10, 2021 10:04 pm

Keeps the aircraft from speeding up too much. It’s easier on the brakes.
 
N1120A
Posts: 26923
Joined: Sun Dec 14, 2003 5:40 pm

Re: Biz-jet thrust reversers activated whilst taxiing.

Sat Jul 10, 2021 10:04 pm

1) I believe they do it to test them.

2) I also think they sometimes use them to slow down taxi to save brakes.
 
Woodreau
Posts: 2172
Joined: Mon Sep 24, 2001 6:44 am

Re: Biz-jet thrust reversers activated whilst taxiing.

Sat Jul 10, 2021 11:33 pm

At my air carrier use of thrust reverser during taxi out is generally prohibited.
 
GalaxyFlyer
Posts: 8576
Joined: Fri Jan 01, 2016 4:44 am

Re: Biz-jet thrust reversers activated whilst taxiing.

Sun Jul 11, 2021 12:04 am

Every bizjet is over-powered; even at near gross weight, a Global will leave the blocks at idle or slight push on the throttles. That and most flights are quite light, so speed builds quickly. A cycle is a FCOM checklist item, too.
 
e38
Posts: 908
Joined: Sun May 04, 2008 10:09 pm

Re: Biz-jet thrust reversers activated whilst taxiing.

Sun Jul 11, 2021 1:16 am

TC957 wrote:
you don't see airliners doing this.


TC957, with regard to airliners not using reverse thrust while taxiing, aircraft with underwing mounted engines have a greater potential for Foreign Object Damage (FOD) when using reverse thrust at low speeds, i.e., taxi operations. The probability of FOD is reduced on aircraft where the engines are mounted higher on the fuselage, such as t-tail design.

As Woodreau mentioned above (Reply # 4), some operators prohibit its use. At my company, in the Airbus A320 series, for normal operations, assuming full reverse thrust was used on landing, we are required to begin reducing reverse thrust at 80 knots on landing rollout and be at idle reverse by 60 knots. We are a also prohibited from using reverse thrust during normal taxi operations.

e38
 
User avatar
CALTECH
Posts: 3535
Joined: Thu May 17, 2007 4:21 am

Re: Biz-jet thrust reversers activated whilst taxiing.

Sun Jul 11, 2021 3:43 am

fr8mech wrote:
Keeps the aircraft from speeding up too much. It’s easier on the brakes.


What fr8mech writes. Cessna Center in MCO, see a whole lot of Cessnas taxing with T/Rs deployed down Alpha,

https://www.youtube.com/watch?v=Z8zqoLN ... l=cpockett
 
CRJockey
Posts: 354
Joined: Mon Feb 10, 2020 11:54 am

Re: Biz-jet thrust reversers activated whilst taxiing.

Sun Jul 11, 2021 1:52 pm

N1120A wrote:
1) I believe they do it to test them.

2) I also think they sometimes use them to slow down taxi to save brakes.


No need to test them but yes, it is to slow down without using the brakes.

And it is used in airliners which have tail mounted engines.
 
TC957
Topic Author
Posts: 4172
Joined: Wed May 23, 2012 1:12 pm

Re: Biz-jet thrust reversers activated whilst taxiing.

Sun Jul 11, 2021 4:49 pm

Thanks for all the replys. Begs the question why engine idle speeds can't be reduced to lower minimums.
 
N1120A
Posts: 26923
Joined: Sun Dec 14, 2003 5:40 pm

Re: Biz-jet thrust reversers activated whilst taxiing.

Sun Jul 11, 2021 5:07 pm

TC957 wrote:
Thanks for all the replys. Begs the question why engine idle speeds can't be reduced to lower minimums.


Works the same with most turboprops.
 
CRJockey
Posts: 354
Joined: Mon Feb 10, 2020 11:54 am

Re: Biz-jet thrust reversers activated whilst taxiing.

Sun Jul 11, 2021 10:00 pm

TC957 wrote:
Thanks for all the replys. Begs the question why engine idle speeds can't be reduced to lower minimums.


Turbomachinery has a certain lowest idle to keep running self sustaining.
That’s why you spin up the core engine with bleed air to a certain extent until fuel can be added to reach a stabilised self sustained engine state.

You want a stable engine on idle power, some margin included. And that happens to create already enough thrust to get the aircraft moving/accelerating.

Not really a problem though in real world.
 
GalaxyFlyer
Posts: 8576
Joined: Fri Jan 01, 2016 4:44 am

Re: Biz-jet thrust reversers activated whilst taxiing.

Mon Jul 12, 2021 12:19 am

CRJockey wrote:
N1120A wrote:
1) I believe they do it to test them.

2) I also think they sometimes use them to slow down taxi to save brakes.


No need to test them but yes, it is to slow down without using the brakes.

And it is used in airliners which have tail mounted engines.


Just looked at the Global FCOMs, cycling the T/Rs is a fist flight of day item on the taxi-out, both the RR-powered 6000/6500 and the GE-powered 7500. Cycle, check for proper EICAS indications and stow.

Also, engines need to idle at sufficient rpm to run 400Hz generators and produce sufficient bleed air to cool the cabin.
 
User avatar
Starlionblue
Posts: 20860
Joined: Fri Feb 27, 2004 9:54 pm

Re: Biz-jet thrust reversers activated whilst taxiing.

Mon Jul 12, 2021 1:43 am

TC957 wrote:
Thanks for all the replys. Begs the question why engine idle speeds can't be reduced to lower minimums.


Because the engines would stop if the mass flow was much lower than idle.

As CRJockey says, it isn't really a problem in the real world. Unless you're in a crowded area or about to turn, you just let the aircraft accelerate to 30 knots, then brake down to 10-15 knots, and repeat the process.
 
Max Q
Posts: 9118
Joined: Wed May 09, 2001 12:40 pm

Re: Biz-jet thrust reversers activated whilst taxiing.

Mon Jul 12, 2021 5:26 am

Reminds me of doing a delayed engine start on the 727 with an inoperative APU one day when I was a very new FE

Captain decides to do this while taxiing, I turn the packs off, he increases thrust on #1 to get the required duct pressure but this increases our taxi speed so he puts #2 into reverse to avoid riding the brakes


It all worked out and as stated you can do this on a rear engine configured type without FOD concerns but it was a bit rinky dink that day
 
jetstar
Posts: 1426
Joined: Mon May 19, 2003 2:16 am

Re: Biz-jet thrust reversers activated whilst taxiing.

Mon Jul 12, 2021 3:44 pm

On the 4 engine Lockheed JetStar bizjet it was a checklist item to test the thrust reversers by deploying them while taxing out to the runway on the first flight of the day. At home base we would normally use a start cart and start all 4 of the engines, but at out stations we would only start engines #2 and# 3 off of the batteries and let the batteries recharge during taxi and then start #1 and #4 so we would stop the taxi checklist at that point where we would test the reversers.

We could have tested all 4 of the reversers without engines #1 and #4 running because the reversers were hydraulically powered by the hydraulic pump on engine #2. Engine #3 had the backup hydraulic pump, but it didn’t supply hydraulic pressure to the reversers, the thrust reverser backup was the stand by electric hydraulic pump which also could be used on the ground without the engines running to deploy the reversers during maintenance.

We never used the reversers to slow the airplane down while taxiing, even with all 4 engines running, just tapped the brakes every so often to slow the airplane down.

JetStar
 
bigb
Posts: 1489
Joined: Fri Nov 07, 2003 4:30 pm

Re: Biz-jet thrust reversers activated whilst taxiing.

Tue Jul 13, 2021 3:21 pm

Used it all the time taxing the CRJ around. Just don’t exceed reverse idle. It does make a big difference on managing taxi speeds without riding and warming the brakes.


Sent from my iPhone using Tapatalk
 
User avatar
CALTECH
Posts: 3535
Joined: Thu May 17, 2007 4:21 am

Re: Biz-jet thrust reversers activated whilst taxiing.

Tue Jul 13, 2021 4:18 pm

TC957 wrote:
Why do biz-jets, especially Gulfstreams and Globals, deploy their thrust reversers whilst taxiing out ? And in sometimes too.
It's that you don't see airliners doing this.
Thanks.


Watching the IL-62 land is quite a sight, deploying the thrust reversers BEFORE touchdown......

https://www.youtube.com/watch?v=N29ZFnQ ... =RyanBomar

MD-80, wheels spooled up during bounce

https://www.youtube.com/watch?v=3mzzt-t ... JustPlanes

TU-154

https://www.youtube.com/watch?v=gybeXt_ ... rgospotter
 
sadde
Posts: 38
Joined: Sat Dec 24, 2016 8:46 pm

Re: Biz-jet thrust reversers activated whilst taxiing.

Thu Jul 15, 2021 12:53 am

Flying both the G-IV and G-V checking the TRs is a first flight of the day item (as someone mentioned above). We also use them to reduce brakewear. Engine parts are paid for on programs that do not discourage TR use, while brakes are exceptionally expensive to replace.
 
TC957
Topic Author
Posts: 4172
Joined: Wed May 23, 2012 1:12 pm

Re: Biz-jet thrust reversers activated whilst taxiing.

Tue Jul 20, 2021 12:08 pm

sadde wrote:
Flying both the G-IV and G-V checking the TRs is a first flight of the day item (as someone mentioned above). We also use them to reduce brakewear. Engine parts are paid for on programs that do not discourage TR use, while brakes are exceptionally expensive to replace.

Thanks for your input , Sadde. So whats the cost for a full set of new brakes then on something like a G550 ? And on average useage, how long does a set last ?
 
sadde
Posts: 38
Joined: Sat Dec 24, 2016 8:46 pm

Re: Biz-jet thrust reversers activated whilst taxiing.

Wed Jul 21, 2021 10:50 pm

65-90k per brake from what I can remember, two per main gear. So, about 350k for an entirely new set. Depending on wear and tear/ pilot taxiing habits I see us replacing a single brake about every 7-8 months on average. They do not wear evenly, so it’s unusual to replace more than one at a time
 
GalaxyFlyer
Posts: 8576
Joined: Fri Jan 01, 2016 4:44 am

Re: Biz-jet thrust reversers activated whilst taxiing.

Wed Jul 21, 2021 11:32 pm

I know of Globals and Challengers have gone years between brake replacements, even a decade at 400 hours per year flying, tho.
 
26point2
Posts: 1133
Joined: Wed Mar 03, 2010 6:01 am

Re: Biz-jet thrust reversers activated whilst taxiing.

Wed Jul 21, 2021 11:43 pm

We're on year 13 with our Global and still the original brakes. 4000+TT with 1500+ cycles. The brakes on a Global are VERY robust. A new set of brakes are in the $100's of Thousands.
 
GalaxyFlyer
Posts: 8576
Joined: Fri Jan 01, 2016 4:44 am

Re: Biz-jet thrust reversers activated whilst taxiing.

Thu Jul 22, 2021 12:53 am

26point2 wrote:
We're on year 13 with our Global and still the original brakes. 4000+TT with 1500+ cycles. The brakes on a Global are VERY robust. A new set of brakes are in the $100's of Thousands.


I didn’t want to brag, but if he’s changing brakes on a Gulfstream every 9 months, something’s wrong.
 
jetstar
Posts: 1426
Joined: Mon May 19, 2003 2:16 am

Re: Biz-jet thrust reversers activated whilst taxiing.

Thu Jul 22, 2021 3:44 pm

I remember in 1980 my chief pilot complaining to me about the $1700.00 it cost to overhaul a brake assembly on the Lockheed JetStar. They were the old fashioned multiple disc steel brakes and would last about 400 to 500 landings, I told him if he wanted to extend the life of the brakes, quit the heavy use of the brakes trying to make the first turnoff on the runway when slowed down enough after the thrust reversers were stowed, let the airplane roll to the next turnoff and go easy on the brakes. On RCA Corporation's JetStar, also based at HPN they had that policy and were getting 1200 landings on their brakes.

Of course that went in one ear and out the other.

On my other chief of maintenance job on the JetStar, we were getting 300 or so landings on the left side brakes and about 450 landings on the right side. He was a very active tennis player and I guess his left leg was more stronger than his right leg and when applying the brakes, either when landing or taxiing he unconsciously applied more pressure on his left leg than his right and caused more wear on the left side. When I told him what I thought about the cause of the left side wearing out faster than the right side, he blamed it on the overhauls, so again in one ear and out the other.

Ah, the joys of being a corporate flight department chief of maintenance and answering to chief pilots who were complete idiots.

JetStar
 
sadde
Posts: 38
Joined: Sat Dec 24, 2016 8:46 pm

Re: Biz-jet thrust reversers activated whilst taxiing.

Thu Jul 22, 2021 4:50 pm

GalaxyFlyer wrote:
26point2 wrote:
We're on year 13 with our Global and still the original brakes. 4000+TT with 1500+ cycles. The brakes on a Global are VERY robust. A new set of brakes are in the $100's of Thousands.


I didn’t want to brag, but if he’s changing brakes on a Gulfstream every 9 months, something’s wrong.


Floating fleet baby! I completely agree.

Who is online

Users browsing this forum: jaybae16, Pellegrine and 19 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos