Idle reverse policy on landing

[Centaurus]

For many reasons, individual company SOP may direct idle reverse after touch-down - unless of course good airmanship dictates otherwise. It may be for fuel conservation, perceived engineering costs or noise-restrictions.

In the CFM 56 series (737), idle reverse N1 is the same as idle forward thrust N1 (nominally 23% N1) - except it takes a bit of fiddling to get the reverse thrust levers at idle reverse without inadvertently slipping into forward thrust. The theory of selecting idle reverse only is that instant full reverse is available should things look a bit dodgy and the end of the runway is coming up faster than planned.

The problem then arises of the relatively long delay in spool-up to max reverse from idle reverse (23% N1) Try it in the simulator and you are looking at 6-8 seconds before full reverse is reached. Because of the extended spool-up period, by the time full reverse is attained the airspeed has probably dropped below 80-100 knots when reverse is not as effective.

I understand N1 remains at high (in-flight) idle with thrust levers closed at touch down and if reverse has not been selected within four seconds after touch-down, the power automatically decays down to ground idle, which works out to be around seven percent N1 less than flight idle.

Presumably this is based on the assumption by the designer that if you haven't selected reverse by four seconds after touch-down then you aren't going to use it and so the power drops back to ground idle (less residual thrust).

The point is this. If company policy is to use only idle reverse for landings then crews should ensure the reverse levers are correctly positioned to give at least (say) ten percent above ground idle in order to permit rapid spool up to max reverse if needed. The spool-up time from ground idle reverse (nominally 23% N1) to full reverse, is significantly longer than the spool-up time from (say) 35% N1 reverse thrust. By selecting (say) 35% N1 reverse thrust after touch-down, the landing roll safety factor is increased with little discernible increase in noise footprint and/or fuel consumption.

Any thoughts?

[Intruder]

Not a good analysis, IMO.

Reverse thrust is most effective at high forward speeds, so you should not try to rely on more reverse thrust as a last-ditch attempt to save a too-long/fast rollout. Also, unless you want to FOD your engines, using more than idle reverse at less than 60 KIAS or so is inadvisable.

At low speeds, idle reverse will remove any residual forward thrust, making braking and steering more effective on slippery surfaces like wet paint stripes.

OTOH, if you want to use more than idle reverse early in the landing roll, then just do it.

[alf5071h]

Centaurus, the technical logic of your argument appears sound, but choosing to have reverse available ‘just-in-case’ might be an ineffective tactical option.
As you say it takes time for the engine to spool-up, perhaps even longer for the mental decision to spool-up to recognise the need for more retardation.
From a landing safety perspective it might be more efficient (safety) to decide to use some higher level reverse as judged in the pre landing briefing based on the reported conditions, or even by SOP, and then during landing when assured of stopping, reverse can reduced to idle. Thus the suggested option of a ‘higher idle’ is moving in a safe direction.
Unfortunately many of the operational decisions are influenced by commercial efficiency, where safety aspects are deferred to late ‘tactical’ crew decisions exposing the crew to the frailties of human behaviour and performance.
Brakes may be cheaper than engine overhaul, but neither compares with the cost of an overrun.

[DrFaustus]

there will be probably no right answer for your question.
Personally I consider the company SOP and most of the time idle REV it is.
Only after having thought about and briefed the landing mass, any a/c unserviceabilities versus available landing distance and the prevailing weather conditions.
On a dry and even sometimes wet runway Idle REV usually is more than sufficient.
If the runway is wet&slippery or contaminated than that is a different story.

Even on a long dry runway with a too long flare I will insist on Full REV being used.

SOP's cannot cover all cases and I think experience and aerodrome familiarity come into play as well, even flight crew recency issues.

Anyhow I think you should think about, brief it and be ready to amend it when necessary, but I do not believe that an intermediate setting (35%) will be a very practical approach.

[decurion]

check out:
Idle reverse versus full reverse thrust: the balance between safety, economics, and noise
Paper presented at the 24th annual European Aviation Safety Seminar (EASS)
Dublin, Ireland, February 29 – March 1, 2012

[Yaw String]

My take on our policy of minimum of idle reverse on every landing,certainly on later boeings is that, even with speedbrake not in the standard "armed" position, the ground spoilers will activate...They will not activate if the speedbrake lever were inadvertently left in the "down" position, with only idle thrust selected...
Also, in the case of a bounced landing, an armed speedbrake may disarm...so, another advantage of always using a minimum of idle reverse on every landing..well..on mine anyway...I think Miss Pamela Anderson would agree with me..sorry Pamela..ouch!

[DrFaustus]

I think this thread is about idle reverse versus full reverse.
Give Pamela a breather and yourself time to have some of that blood returning to.......

[FA10]

With autobrake 1-2-3 on a runway with good braking action reverse thrust above idle does not give you any advantage in relation to landing distance.
As soon as reverse is starting to assist in the deceleration, the pressure on the wheel brakes is being reduced, as autobrake is looking for a certain deceleration rate. So in normal circumstances reverse thrust is only easing the use of the brakes, which keeps your brake temperature nicely under control - however your landing distance will be exactly the same with or without T/R.
Things are different in autobrake max, max manual braking or runway conditions where anti skid is going to operate: 2nd or 3rd detent is going to give you a nice reduction in landing distance (if you instantly use it, as it was already said before...)

[Sciolistes]

And there is no way of knowing what your min turnaround time is with idle reverse. Numbers only for no reverse and 2nd detent.

[BOAC]

I cannot quite understand the 'aversion to'/issues with idle reverse

1) as FA10 says, the deceleration will be identical with and without reverse if autobrake is used, and

2) LDAs are checked for the reverse idle condition.

The only time 1) is not true is when braking action is compromised, when you would not be using reverse idle anyway.

As Dr F says , by the time you might realise you should have used it, even from a high idle you have troubles.

[Wizofoz]

And there is no way of knowing what your min turnaround time is with idle reverse. Numbers only for no reverse and 2nd detent.

Both our QRH and OPT cover Idle Reverse for Brake Cooling calculations.

[stilton]

Idle reverse is a bad habit. It builds a 'muscle memory' and a mentality that has led flight crews to not use full reverse even when it is needed.


More than one runway overrun has been attributed to this.


Certainly the autobrakes will 'back off' to provide the requested deceleration rate when full reverse is used.


That is fine, unless you get the reverse in at higher speeds it is far less effective anyway. Once you have selected max rev you can brake as necessary.



This allows maximum use of all braking / deceleration devices as they are most effective.


Remember when this was standard ?



I have flown with more than one FO who was afraid to use max reverse even when required, concerned he would 'break something' or use an extra 100 pounds of fuel.



I use max reverse on every landing and brake as necessary, I know you will go on about carbon brake heating, so what, who cares about the brakes when you are off the end of the runway ? :eek:

[Wizofoz]

More than one runway overrun has been attributed to this.


Really? Can you name one?

This allows maximum use of all braking / deceleration devices as they are most effective.


So do you also use max braking every time?

[chimbu warrior]

Really? Can you name one?


Qantas, Bangkok, although there were (as usual) other factors involved. It is for the very reason that other factors arise that I believe no manufacturer advocates idle reverse, although I am sure they are aware of individual operators who endorse such a policy.

One over-run negates the savings of a thousand idle reverse landings.

[Old Fella]

Certainly other factors were involved in the QF overrun at Bangkok. Where to start? Contaminated runway, landed long and hot, lack of communication between LH & RH (Handling Pilot) seats, 25 Flap, Go Around countermanded without notification, one thrust lever left "stood up" and developing around 1.50 EPR during aborted Go Around before being retarded, Full Reverse not used, off the end at 88 Knots. From memory, less than ten observed actual Full Reverse landings between the three cockpit crew and few Full Flap landings. For mine using Reverse is like using Carby Heat. All symmetrical available, Full Reverse / Full Carby Heat or nothing.

[Yaw String]

The outspoken wisemen have had their say...instantly condemning those who do not subscribe to their views...so, name some more of my bad habits..well, apart from shaking Ms Anderson's breasts on that bounced landing!

[DrFaustus]

Idle reverse is a bad habit. It builds a 'muscle memory' and a mentality that has led flight crews to not use full reverse even when it is needed.

Valid point, but if you do a hands on drill and actually simulate what you are intending to do, then you retrain yourself. I always do it, before lining up a touch drill for your unlikely RTO and inflight for your landing

More than one runway overrun has been attributed to this.
exactly it was a contributing factor, but usually they did not fully deploy them after they were either hot&high and overflared

Certainly the autobrakes will 'back off' to provide the requested deceleration rate when full reverse is used.


That is fine, unless you get the reverse in at higher speeds it is far less effective anyway. Once you have selected max rev you can brake as necessary.



This allows maximum use of all braking / deceleration devices as they are most effective.


Remember when this was standard ?



I have flown with more than one FO who was afraid to use max reverse even when required, concerned he would 'break something' or use an extra 100 pounds of fuel.

Well that is a training issue as far as I am concerned. During their line training the trainers will surely have covered an important topic like that. Breaking something and fuel saving are most certainly not mentioned in a training curriculum as reasons for not using a thrust reverser. If your FO mentions those reasons on the day why not talk about it and let him have a go

I use max reverse on every landing and brake as necessary, I know you will go on about carbon brake heating, so what, who cares about the brakes when you are off the end of the runway ?

I calculate my landing distance that gives me a feel for how much extra distance is available and also what exit point is possible (sometimes ATC throws a vacate via....at you with the landing clearnce). If there is a lot of extra runway available I follow my company"s SOP, if not I use full reverse. But I mentioned it before there are many ways to accomplish the task safely. The same principles are valid for reduced thrust take offs, we don't do full rated thrust TO all the time do we?

[barit1]

I have flown with more than one FO who was afraid to use max reverse even when required, concerned he would 'break something' or use an extra 100 pounds of fuel.

That extra 100# is the premium you pay for the insurance policy against an overrun.

[Wizofoz]

That extra 100# is the premium you pay for the insurance policy against an overrun.

Then why don't you also use maximum braking, even if it's a dry, 4000m runway?

It's only IF you use maximum braking that reverse has any effect on your stopping distance.

[BOAC]

I'm pleased it is not only me challenging this 'fooey'. 'I always use max reverse' - :p

Very popular on a 10000ft runway with an exit point at the far end, I guess.

It's called airmanship. You plan the deceleraton method to suit the LDA. I have in my time, paying lip service to the QAR, opened the reversers at idle and then cancelled them to avoid having to apply power to reach the turn-off point on a long runway. According to some here I should have screeched to a juddering halt with TOGA reverse, and then blocked the runway for 2 minutes while I taxy the other 6000'. Yes, as wiz observes, I should also obviously have been using max autobrake as well Doh! Little wonder we are seeing the accidents and incidents that are occurring. Where are these people learning to aviate?

[ImbracableCrunk]

How many over-runs occur when the plane touches down in the TDZ? . . .

[safetypee]

I C; and the definition of TDZ is …
ICAO definition.
Runway marking definition.
Performance definition, Boeing definition, or
the practical and required definition to provide adequate safety margin during landing.

[BOAC]

We could just settle for the first 1/4 or 1/3 rather than getting into a-r definitions?

[safetypee]

BOAC, you might settle on a simple rule of thumb – type dependant, but it wouldn’t work everywhere; try the first third at LCY !! (Don’t). The important aspects are in the details, 'a and r'.
Another disadvantage is that if rules of thumb (RofT) are used as a ‘sop’, then this can reduce the perceived need for knowledge of landing performance and its dependencies, variables, etc, and reduce the crew's ability to calculate the actual landing distance required, i.e. not understanding the circumstances when the RofT must be ditched.
Conversely, with exemplary knowledge, and due consideration of the variables, the landing distance calculated can be checked with a RofT.
Pilots need to be encouraged to think about the problems and then check afterwards, a similar idea in some posts above about the use of reverse; if you are going to select it, then use it all.

[BOAC]

Related to ssg perchance?

[Wizofoz]

if you are going to select it, then use it all.

Saftey-

It's interesting that neither you nor anyone else will answer my query- if you think it necessary to use full reverse on every landing, why not also full brakes?

[rudderrudderrat]

@ safetypee.
if you are going to select it, then use it all.
Then how do you comply with Notes
"1.2.3 REVERSE THRUST
More than idle reverse shall not be used except for safety reasons or if necessitated to comply with ATC reuest" at LSGG, or
"1.2.2. REVERSE THRUST
Avoid use of reverse thrust after landing between 2330-0600LT except for safety reasons" at EGKK etc. etc.

Is that the real reason for the safety pee?

[White Knight]

First 1/3... 330 or 340 (3,5,6) no problem............

If you can't stop with idle reverse and min autobrake you're a puss!!!!!!!!!!!!!!!!!!

Trust me:cool: says 7,000 hrs on type:cool::ok:

[BOAC]

if you think it necessary to use full reverse on every landing, why not also full brakes? - and, as ssg would say, full power on every take-off (if you are going to select it....etc) and we might as well tank to RTOW every sector just in case - well, you never know? Unbelievable. One has to hope this is not filtering through to training.

[safetypee]

On reflection, #24 was glib - conceptual rather than absolute. There are few if any absolutes in aviation.
The concept of ‘use it all’ is similar to the mindstates of ‘how can we land’ vs ‘should we be landing’ in a pre-landing assessment. The objective (the latter) is to encourage crews to be aware of the assumptions in landing performance and thus the limitations of their landing decision.

Many overrun accidents involve misjudgments of the conditions or a poor choice of action. If these occur in combination with large, but normal variations of operating performance – unstable approach, high over threshold, landing fast, long, delayed deployment of spoilers, etc, then the risks of an overrun increase rapidly.
It should be possible to identify these risks and mitigate them before landing by deciding to change the planned level of braking and/or use of full reverse – a strategic decision. Any later identification of the need to change plan involves a ‘tactical’ assessment and is often complicated by time/workload pressures. This assessment often occurs when well down the runway, and approaching or exceeding the point of being able to prevent an overrun.

Certificated landing distances are based on the use of max braking with an added distance safety margin (factor). This margin “accounts for the normal operational variability that can be expected in day to day service such that the chances of a landing overrun are remote” ( Landing Performance Large Transport Aeroplanes (www.ead.eurocontrol.int/eadbasic/pamslight-EFEEB9AA018E1010EE17C973765EA138/7FE5QZZF3FXUS/EN/AIC/P/014-2006/EG_Circ_2006_P_014_en_2006-02-02.pdf)).
Thus if landings were routinely made at the limit of pilots’ variability, and on limiting runway lengths, max braking would be required to minimize the risk of an overrun to a chance less than ‘remote’.
Fortunately most pilots constrain their variability, and in general do not routinely land on limiting runways (ex LCY etc). However, this apparent normality in operation can lead to complacency.
Using the concept of max braking can minimise any additional risk from complacency, unexpected variability, misjudgement, misassessment, or poor plan of action. When a landing decision chooses not to use max braking, crews should have an improved awareness of the associated risks and mitigations for that landing, i.e. the crew thought about them before changing the ‘sop’ (max braking standard operating plan) to an acceptable alternative.
Brake for safety not for comfort.

Reverse is not normally considered in certificated landing performance due to reliability / consistency problems (CS/FAR 25.125).
If crews assume that the safety of a landing could be maintained by ‘late’ use of max reverse, based on their assessment of the situation, then there is some (significant) risk that reverse might not be available/used when required – and at a time/position on the runway where it would be effective.
Here, the concept of planning to use max reverse (‘sop’) can reduce these risks by checking that the ‘emergency late use’ of reverse will be available – that the system has deployed and the engine has spooled up immediately after touchdown. If reverse does not work, then braking can be increased much earlier to minimise the risk in the event of other problems – as above.

Use of reverse vs environmental impact should be considered as a separate, but important safety issue of conflicting goals and objectives. See refs to ETTO - efficiency / thoroughness tradeoff.
The frustrating point is that local authorities duck their responsibility for safety by placing the decision on operators and pilots.

[sheppey]

It's interesting that neither you nor anyone else will answer my query- if you think it necessary to use full reverse on every landing, why not also full brakes?

I must admit I am unsure if you are just taking the piss or dead serious. I assume the former. Hence lack of anyone taking you up on your comment. Max brakes on most landings at max landing weight will cause red hot brakes and danger of not only fuse plugs eventually letting go, but deflated tyres etc. In addition if max brakes used as a matter of company policy (never happen) few discerning passengers would ever choose your airline again. The seriously uncomfortable deceleration with max brakes can be alarming to passengers as can passenger evacuation with burning brakes. . On the other hand, full reverse may be noisy on some types or hardly heard on others but the decel is bearable and relatively benign. On a wet surface runway, full reverse is vital where wheel brake efficiency is less than optimum.

[alf5071h]

Sheppey, re “Max brakes on most landings at max landing weight will cause …”
You present a fairly definitive position, which for many aircraft types is incorrect.
What about the much higher energies in a MTOW RTO; then the conditions you quote might be encountered. Even with hot brakes etc, the certification regulations require that there is no significant hazard; e,g, a brake fire in tests should be allowed to exist for 5 min before extinguishing.
Many people make erroneous interpretations from sensational graphic images, which if recalled from memory during operations can adversely bias situation assessments and subsequent actions.

High decelerations may be encountered when landing on a dry surface with max brake, but with anti-skid in wet conditions the deceleration would be most acceptable – as well as very necessary to stop safely.
Use max reverse, but don’t discard max brakes when required, particularly at lower speeds.