Haroon,

It's just a bit of maths.

You need to land in 60% of the available distance. That means you must have 1/60x100 of your actual landing distance available. That's the same as 1.66 recurring so 1.67 is used.

For a wet runway we must have 115% of the dry figure so we could do two calculations or we could simply calculate 1.92 X actual landing distance.

For a test pilot actual landing distance = unfactored landing distance. And in many companies this is what is used for line operations.

It could be argued that as we know the average line pilot is not likely to meet the test pilots results we should use more to fully comply with the spirit of the law but you wont find many(any!) operations that include a line pilot factor.

Inverting the safety factor numbers may be "just a bit of maths," but it serves to confuse more than anything else. In these forums, using the numbers actually cited in the various regulations would be a much better idea...

Problem with the various regulations is they are not consistent themselves. Aviation is a profession with a few numbers - a bit of simple maths shouldn't be beyond anyone here! :hmm:

Yes, but a simple cite, such as "adapting/inverting the rule from OPS 1.515..." would serve to clarify.

Aviation safety requires avoidance of unnecessary risk; risk depends on the hazard, frequency of encounter (likelihood), and the severity of the consequences. The process (risk assessment) requires judgment, which in turn requires dependable knowledge and appropriate skills of thought.

A safety factor provides a buffer between the hazard and the planned operation. It is a margin for ‘error’ or deviation from the ideal to minimize the risk(s) and/or alleviate consequences of the hazard.
Haroon discusses ’ the ‘ safety factor (#34), but the issue is ’ a ‘ safety factor, relating to a specific situation and the assumptions made about human behavior/capability (in that situation). Hence, in an emergency (change of situation), the landing-distance safety-factor can be reduced. Note that although a wet landing uses a landing–distance factor of 1.92 it is not necessarily the same safety factor as for a dry runway as the increasing number of the accidents indicates.
Thus, the debate is firstly whether the event is an emergency or not – it’s not; and secondly if an over weight landing were to be attempted what distance is required to provide a margin of safety equivalent to a max wt landing on a dry runway.

EU-OPS 1.475 requires a 1.67 factor (normal operation – in flight replanning).
The QRH actual landing distance (5700ft) is probably shorter than the certificated actual landing distance because reverse detent is used (I assume that this is idle, vice ‘max reverse’ quoted elsewhere in the QRH).
Thus by adding 220ft (QRH adjustment for no reverse), the certificated actual (overweight) distance is ~ 6000ft.
A 1.67 factor would require ~ 10,000ft runway.
However, this calculation does not consider other / new risks such as brake energy limit, brake fade, landing gear limits (vertical rate and side loads).
As all risk assessments should be specific to the situation, the calculations for the overweight landing above does not use an equivalent basis as a for max wt landing, and it is these differences which might sway the argument for not landing overweight without an emergency as the aircraft is not certificated for this on a regular basis.

Re The flight safety foundation have a good briefing. (F E Hoppy), is this the one? http://www.skybrary.aero/bookshelf/books/874.ppt

A recent FSF report outlines the nature of the risks, but provides few practical remedies - http://www.skybrary.aero/bookshelf/books/900.pdf
A similar but more practical document is ‘Runway excursions’ by ASTB.
For some ‘How To’ aspects – Judgement etc see Aviation.org, - ‘library’ section, presentations on Critical Thinking, Situation Awareness, and Decision Making (free registration required).

Safetypee,

I was refering to this:
Approach and Landing Accident Reduction (ALAR) | Flight Safety Foundation

Well worth reading through the whole thing for those with a little time to spare. Section 8 is most pertinent to this discussion.

Hello again. Sorry for the late response as I got stuck in a busy pattern after the sim.

FE Hoppy thanx for the reference I was looking for. Perhaps I did'nt pay proper attention to the terminologies used i.e "Margin" and "Factor" in my last post.

If I have understood correctly now then to land within 60% of the landing distance available means 40% of the landing distance available will be there for us as a safety margin.

i.e. If landing distance avaialble is 10,000 feet then aircraft has to stop
within 6000 feet so that the remaining 4000 feet is avaialable as a
safety margin. The remaining 4000 feet is 40% safety margin in
reference to landing distance available and 67% safety margin in
reference to landing distance in which the aircraft stops.

Thus in reference to the aircraft actual landing performance

Margin of Safety = 67%

Safety Factor = 1.67

Whereas in reference to landing distance avaialble the margin of safety = 40%

Thankyou all :ok:

if pax are calm, and no one is hurt, i would hold and land within max landing wt, course I'd check wx, talk to the company and everything, but I wouldn´t land a 737 or a 320 with 7 tons overwt, at night, out of a non precision approach, JUST to save fuel. Again if there´s one good reason to land overwt, eg a pax not feeling well, weather deteriorating really bad, I´d think about terminating the flight, otherwise I´d burn off fuel.

A very interesting thread, and a worthy Techlog discussion :D

I cannot add much more in the way of wisdom, but perhaps can help simplify it or provide a 'take-away' point.

1. Decision maker's rule of thumb for attempting an Overweight (over MLW) landing:

"Is the hazard of continued flight, greater than the hazards of an overweight landing?"

The hazards of the overweight landing having been identified by FE Hoppy, JT and others. Especially the exponential increase in energy that must be absorbed by the gear and airframe on touchdown (Vg Max) and then dissipated via braking systems. Also, beware the temptation to overestimate one's capabilities to 'handle' an abnormal situation.

If you can't dump the fuel, and nobody is likely to die or be injured by your holding 1hr or 2 hrs -- hold.

2. "Make fuel on the easy days. Not the tough days."

If your airline is like our airline, the focus on reducing carriage of 'discretionary' fuel and routinely uplifting Minimum Operational Requirement across the network, every day, will have more than offset your burning 4 (or 20) tonnes the one day you may be called to do that.

3. Overweight landings are different from 'not full factors' landings.

You may also be faced with the situation where you are at or below structural MLW, but forced to consider putting your aeroplane into a field that does not meet the 'full factors' 1.67 (dry) or 1.92 (wet).

In that case, you have eliminated one unknown - you will have landed your aircraft at that weight many times before. You are in familiar territory, handling-wise.

But halving the factor, is quartering the margin for error.

If, after considering the italicised advice, you need to put your aircraft onto a runway that has less than full factors, you have a situation that your cabin crew, your pax, and the airfield services ought to be briefed in on. The subsequent landing will not be pretty, braking may be forceful, and any handling error on your part might have you off the fairway and in the rough. Literally.

My 2c worth.

Great discussion. :D

Overweigh Landing extremely simple
 

Dear all

An overweight landing assumes there is no time for dumping or dumping is not possible.

There is no regulation that requires factoring.

As a guideline: runway, climb and obstacles limitations need to de taken into account.

Overweight combines adversely with any system failures that affect deceleration and/or controlability.

Piece of cake.

True for you perhaps, but lack of regulation does not mean, do what you like.

Would you fly with 0% variable and 0 minutes fixed fuel reserves, if there were no regulation? What would guide you in your decision on fuel reserve, if there were no regulation?

We still have a duty of care. We all know that we are not all test pilots flying in controlled test conditions. We know that, and the court of inquiry will know that too.

How do you assess it, if not by reference to factors implied by regulations as being a suitable standard?

Do you use another method? One that can stand scrutiny?

I ask out of curiosity, not rhetorically - factors are treated as in-flight requirements as well as pre-departure requirement over here.

Its up to the sound judgement of the captan.

And yes I do have some good guidelines that have been found sound by various chief pilots of mayor flag carriers.

Ask Emirates Airlines it they can stand up that challenge.

Ask Emirates? They are not here. You are.

Why the reluctance to share?

You want the knowhow, you pay for it...... ask your chief pilot, he gets paid for it I hope.

49 yo and still has not learned to play well with others.... :bored:

Mod - no worthwhile contributions here from the probationer... shall we tidy up those last few posts?

ITCZ: Its not a game.

You will find out the day you ever have to take a serious decision. My post regarding overweight landing is correct and reflects the current state of rules and regulations.

Any margin that a company wants to build in is at their own discretion and policy.

You referred in your post to a possible court investigation if something would ever go wrong, I thank you for that remark. I hope you are able to asses that implication wisely and pass it on to whoever you fly with.

I took the decision to share the extend my experience with whom I like and there is nothing wrong with that.

By the way I even have a method that makes your decision completely independent of braking action and malfunctions in the brake system but not for you.

ITCZ: Thank you for the PM. If you claim to have 24000 hrs and be a Chief Pilot it should be easy for you to put in cristal clear language your vieuws and policies regarding overweight landings. I hope I can learn something from it but at a certain moment the learning stops and the teaching starts

Thankyou SuddenWinds, ITCZ and Pitch Up Authority for your posts.

Pitch Up Authority:

You mentioned that,

But the company minima cannot be below the regulatory minima, please correct me if I am wrong.

Secondly you mentioned that,

But as pointed out by FE Hoppy earlier in this discussion JAR OPS 1.475 and 1.515 states the regulation which requires this factoring for in flight re-planning (if there is no emergency).

Though I am not a test pilot but I am optimistic that I would be able to land within the landing distance available in conditions which are mentioned in this post. I believe even those who say they wont land in these conditions are able to do so.

But we are not optimistic about the fact that absolutely nothing can go wrong. It is very much possible to enter the Caution Zone after landing (if nothing else goes wrong) and if a tire deflates and one is unable to vacate the runway then is there something that will protect us from the legal side :ugh: especially when the regulation does not allow us to land unfactored.

Things can go wrong even after full compliance with the regulations but at least we are legally covered. So basically at this point of discussion we are trying to focus more on the legal side because we need protection on that end apart from passenger and flight safety.

Its about our own Safety NOT that of the passengers
 

One of the shortcommings in ATPL courses is that there is not enough atttention for the background and reasoning behind certain rules, regulations and limitations. (ex Crosswind limitations, validity of friction coeficients etc....)

It looks like these gaps are sometimes covered by operator trainig programs and manufacturers efforts to inform pilots more than they have done in the past. Technical commisions within pilot unions try to do the same but these organisations have often very limited resources.

Individuals that were and are member of ICAO and JAA performance comities have addressed certain topics but have also highlighted some of the shortcomings of the regulatory proces.

There are a few things we can do but this is not the place.

In the end its about our own safety, nobody can ever accuse you of putting the safety of your pax at danger except a corrupt system.

Its good to know the background but once a regulation is made it has to be followed regardless of the reasoning behind it. I mean if a policeman catches me on crossing a red light, I cant argue that I should not be punished on the basis that I didn't bang into any other car, as collision avoidance was the main reason of traffic lights at a crossing.


There are shortcomings because regulations are made by humans and one cannot rule out human factors/limitaions. But to challenge a regulation one has to submit evidence against it to the concerned committee so that a revision is issued. Until the new regulation is issued the previous one remains valid in the court of law.

Legal Implications + Corrupt System = Nightmare :{

What if the car has a technical problem?

Not all situations are covered by regulation.


I agree

During normal operations I used to (were possible) decelerate with reversers only. After a while you get a fairly accurate idea what lenght you need as function of touch down ground speed. This method makes you independent of brake system problems and breaking action. The only problem is the reliability of the reversers as function of system reliability and the combination of braking action/ crosswind.

It puts the advisory data for slippery runways in another context. These data are subject to fierce discussions at all levels. Directional control problems as a consequence of uneven braking being one of them.

Basicaly you can always land on the runway to took off from if it is dry. Max brake energy may be a limitation.

If it is not dry you better look carefully at groundspeed on touchdown and slope when you choose your RWY. This becomes more important on slippery runways. Those who live in the northern part of our globe know all about this.

To all,

I thought I would add a couple of points which I have not seen in the preceding discussion (forgive me if I have overlooked them).

The point has been established that the factoring of the actual landing distance is a dispatch requirement, i.e., a 6000 foot actual landing distance requires a 10000 foot runway under dry conditions. Further we have established that under wet conditions, an additional fifteen percent mist be added, thus requiring 11500 feet.

We have discussed whether this remains a requirement after dispatch. The conventional wisdom is no, it is not a requirement following dispatch. It is a planning requirement only.

In the US, a lesser known requirement resides in Operations Specification C054. This addresses the lower-than-standard minimums case (standard meaning RVR 4000 or 3/4 mile). The relevant text is:
Note that this is an operational, inflight requirement. The PIC shall not begin an instrument approach, etc. It turns out that the "appropriate" section of the CFR is 121.195(b), making this requirement identical to that in 121.195(d), which is the 115% requirement. So the requirement is the same, but the threshold criteria and the point in the flight where it is invoked are different.

This would seem to suggest that there is an argument to made supporting the use of the dispatch landing distance requirements while in flight.

I was curious to see whether the JARs contained a similar requirement. Perusing through JAR-OPS Part 1, I could not see any such requirement...which, given my lack of familiarity with JAR, isn't saying much. However, I did note the following requirements regarding landing distance in JAR-OPS 1, Subpart G, Paragraph 1.515:
Again the language requires the PIC to make an assessment, before commencing the approach, that the dispatch requirement can be met.

These seem to be two instances which are not consistent with the interpretation that the dispatch requirement goes away after takeoff. Neither directly apply to Haroon's initial scenario, but these things have a way of laying the foundation for the arguments during the hearing. All of which leads us back to John Tullamarine's point that you really need to justify non-compliance with the landing weight by declaring an emergency. Thus, you need justification beyond commercial purposes.

That said, I'll add my two cents regarding the real thing. Based on my very nearly disastrous experience with an overweight 767-300 returning to the departure field, I can state that non-precision approaches at night are probably not the best time to abandon the factoring criteria. Although we had the factored distance for our weight, the maneuvering required after breaking out at five hundred feet and 170 knot Vref put us well past the touchdown zone at an radio altitude of zero (based on the DFDR later reviewed). This necessitated a go-around, which was followed by an immediate failure of the flight directors, which was then followed by a 2000 foot ATC-instructed level off, which directly led to a flap overspeed. Having gotten that sorted out, the ensuing landing, in the touchdown zone this time, led to three of eight main tires failing.

All three of us (I was the non-flying FO) made a remarkably complimentary series of errors that night, which very nearly used up all of the margin that we had. Overweight landings need not be disasters...I've made others that were far less dramatic...but they open the door up to margin-absorbing non-routine irregularities. Although you can and should plan thoroughly and comprehensively, you retain the margins whenever possible because you will never, ever, see the one coming that gets you.

I agree, dispatch requirements apply when airborne under JAR.

Nice example of where ATPL courses and training should focus on.

Given the same rwy lenght I would take the side with an upslope even if it is a NON Precision app, check the numbers in the AFM.

As a commander you need to be able to put the acft on the right spot.

There is no need to use max brakes but brake as function of runway lenght.

This is what EK did wrong in Johannesburg.

All this is written down in the FCTM, no secrets.

Mansfield, #61, some interesting items.
For info; JAR is now EU-OPS, but the text is essentially the same.
EU-OPS and FAR 121 are slowly being harmonized; the landing requirements are essentially identical and originate from the same certification requirements CS 25.125 / FAR 25.125. The only significant difference is in contaminated operations where EU-OPS 1.520 requires accountability but FARs do not. However, FAA SAFO 06012 does refer to the difference.
CS 25.1591 ‘Contaminated Runway Certification’ is well worth reading as it provides most of the definitions and assumptions for the operation; one significant point is for operators to determine whether reverse is credited or not.

Pitch Up Authority, re the choice of runway direction, perhaps the head/tailwind – groundspeed might be the dominant consideration. After all it is energy (speed squared), which has to be dissipated within the runway length.

Re There is no need to use max brakes but brake as function of runway length.
Perhaps this is a bold generalisation as it assumes that pilots know what the limiting landing distance is and thus the additional safety margin available from a longer runway.
Unless an operator’s landing performance covers a range of runway distances (usually only the distance of the chosen runway), the crew will only know if they meet the landing requirements or not - yes / no choice.
Landing data is provided for weight (landing mass). A better guide as to how hard to brake can be obtained by comparing the max allowable landing weight (on a given runway) with the actual landing weight, but this too might not consider additional margins on very long runways.
Weight comparison provides some guidance as to the safety margin available, but this still requires experience, and consideration of runway conditions and other variables before choosing a level of braking. Some data (and aircraft systems) provide some of this information, but all, as do humans, have limits of not knowing the precise nature of the conditions, thus rules of thumb such as initially brake harder than you judge might apply.

From your post #60, the reliance on reverse might be foolhardy (cf Midway accident). Normal landing performance rarely credits reverse thrust for good reason. Being ‘independent of the braking system’ is a risky mindset, particularly on slippery runways after cancelling reverse.

Similarly, you may have generalised the phrase ‘the advisory data for slippery runways’, but in EU-land the data required is much more than advisory; see above EU-OPS 1.520, CS 25.1591.

Safetypee: I agree with your statements and I do not see where I stated anything in contradiction.

I you land on a 3000 m runway with a 737 using rev only you take no risk at all. At 120 kts you need 1600 m and at 140 kts about 2000 m to get the speed down to 80 Kts. Nice to know that you have some brakes on top of that if they perform as predicted. Crosswind and directional control are crucial as you may have to stow the rev but all that is part of your assessment.

JAR OPS as opposed to FAR did go one step further by requesting data for slippery rwy with a 15% factor. The problem is the reliability of the friction measurement. See briefing from Boeing on that subject.

I made myself a table based on the AFM with landing data for various overweight conditions including Vmbe limitations. If you look at them on a regular basis you develop a good feeling what is possible.

Groundspeed is a key factor as I had stated before. If rwy is slippery, slope becomes significant.

When driving a car you know how to decelerate as stop before a traffic light. With an aeroplane it just takes a while to get the same feeling but it takes some effort. You need to take some time after each landing to reflect a bit on what happened. After a while it becomes second nature.

A useful exercise on a very long runway is also: Idle rev and no braking and see how she decelerates by herself, you will be surprised.

Thankyou all for your inputs

According to " JAR / EU-OPS 1.475 ", 1.67 factor for dry runways remains valid for inflight replanning.

Is there a FAR reference like this?

Returning for an overweight landing is not 'inflight replanning' as I understand it. That is a defined procedure usually for medium/long haul flights to re-plan a destination if you are struggling for fuel at the initial planning stage.

In any event in my very large EU Ops airline the requirement is not the same once airborne.