Reverse during taxi
 

Hi all,

Good someone please explain to me the use of idle reverse thrust during taxi as an alternative procedure to braking. Apart from possible fod ingestion are there any other disadvantages? is this practice prohibited? I referring to the B737 CL and NG series.

Thank you in advance.

Generally idle reverse isn't used for braking during taxi. Reverse is most effective at high speed. FOR ingestion is also a problem. Different airplanes,airlines and manufacturers have different restrictions, but generally using reverse during taxi is either not recommended or prohibited except for emergencies when brakes are inoperable or the surface is so slippery brakes are ineffective.

Not a good idea on a/c with wing mounted engines but quite common to see biz jets like Gulfstreams taxing about with one in reverse to limit taxi speed.

Some operators of types like the MD80 back themselves off the gate using reverse thrust or at least they used to in the US.

On aircraft like the 744 and 777, you will lose your V-speeds for takeoff if reverse is used during the taxi out. Best only used in that situation if necessary for control reasons such as on slippery surfaces. I wonder if the newer 737's are the same.

Used to use idle reverse on engine #2 on the 727 although I'm sure all three engines could be used if desired.

Loss of V-Speeds ???
 

JS, on what basis do you loose your V-Speeds if reverse were to be used during taxi out? I am intrigued by that statement.

Pax here but I remembered quite well back in December 1989 when Romania was under communist control that on longish taxi on 732 in Brussels (European Airline) the reverses were used during taxi - they were so obvious on those aircraft. During my visit to the FD, the captain stated it helped the breaks during the taxi out.

Thanks for the quick replies,

I'm sure this has been debated for some time. To cut a long story short we getting hot brakes and the lifespan of these brakes are not good. Some guys have reverted to using idle reverse thrust on long down hill taxiways. Their brakes are cooler. But of course one fod incident will cancel out this attempt to save the brakes. Are there any airlines that do not prohibit this practice?

How about single engine taxiing as a way of keeping speed under control? No FOD problems, less thrust, reduced fuel consumption, less engine hours etc.

Until JM comes back- I can't find a FCOM reference but certainly in the event of an RTO in the sim on both the aforementioned types the V speeds are "wiped" from the FMC, quite what the trigger is ( RTO autobrake operation, REV Thrust being selected, or sim re-position) I'm not sure...

PM

In the context of taxiing to the runway for take off FWIW on some types (certainly at least one heavy I know of) there is a limitation that you can't single engine taxi if you are above Maximum Landing weight

A little bit surprised at this statement as because the reversers operate in the vertical plane its going to be stirring up a lot of FOD that is likely to end up in the engine intake.


On aircraft like the 727 or Falcon 50/900/7x using the centre engine where the reversers operate in the horizontal plane you wouldn't have that problem

Used to be quite common. Lots of videos on-line.

https://www.youtube.com/watch?v=-Zkxh903s_w

Procedures need to be approved by the Chief Pilot if they're not stated in the manuals People doing their own thing points to poor discipline and leaves your​ head on the block if anything goes wrong.

From Ground Ops 2.5 in an old Qatar 777 FCOM:

Loss of V-Speeds ???
 

KRviator. Thank you. As one from an earlier time I did not pickup on the real meaning of the comment, i.e. that the V-Speed display would be lost. I thought the inference was that the originally determined V speeds, which would be set on the bugs in my era, would become invalid because of having applied reverse.

I've noticed larger business jets, the G-V and such, often use reverser on one side. I suppose it's to reduce wear on the brakes.

KRviator

Many thanks for the reference, makes sense. I may have missed it but I can't find similar in our current FCOM or FCTM so I suspect if it was ever there it has been edited out.

Only once off the gate on an FAA checkride on a 727. DFW at night. Many many moons ago. Never used it again there or anywhere else. Not a good procedure

There's a requirement by law for the reversers to be visually checked stowed before the take-off. This is usually done during the pre-flight walk-around inspection. Once you used your reversers you must check them visually again, if you are unable to do it from the cockpit/cabin (as the case be with many airliners) you need to stop, shutdown, get out, do a walk around and then continue. Not very practical.

Last time I used it on a jet was on the #2 on an L-1011 TriStar at Gander taxying out for departure a long long time ago; it was approved practice.

After a lengthly debate with the Captain about use of reverser on taxi, the reverser then refused to re-stow correctly when commanded. The ensuing headaches afterwards convinced me that it's best to leave them until you get to the landing runway!

They use a chalk test to determine relative reverse thrust levels vs aircraft speed to visualize the reverser efflux flow and potential for ingestion.

These visuals show that the small pieces of chalk are blown forward off the tarmac too far to be ingested especially when the aircraft is backing up.

At high landing forward speeds they are overrun before they bounce off the runway unless of course you eject too much efflux at lower speeds. If this is the case then you definitely want to be over a runway blown clean by other aircraft operations