Inflight re-planning and application of regulatory factors

[Haroon]

Hi

My question relates to the following scenario:

Dispatch has planned for a destination that is forecast to be dry (i.e. with a regulatory factor of 1.67 for jets).

On arrival there is rain and runway is wet.

After recalculating the landing distance, is there an in-flight requirement to apply the wet regulatory factor of 1.92

Though primarily these regulatory factors are a dispatch requirement but according to some, as long as it is not an emergency (land ASAP) situation these factors needs to be applied even in flight.

I am trying to find the ruling about this issue according to FAA and JAR/EUOPS.

Is there something in black and white?

Regards

[Fullblast]

Once you're in the air you must use actual informations and plan accordingly, factorization not legally required. JAR OPS 1.400.

FB

[Haroon]

Thanks Fullblast

I searched for the reference you provided through google, it does'nt really mention anything specific about the factors:

JAR-OPS 1.400 Approach and landing conditions (See IEM OPS 1.400)

Before commencing an approach to land, the commander must satisfy himself that, according to the information available to him, the weather at the aerodrome and the condition of the runway intended to be used should not prevent a safe approach, landing or missed approach, having regard to the performance information contained in the Operations Manual.

IEM OPS 1.400 Approach and Landing Conditions (See JAR-OPS 1.400)

The in-flight determination of the landing distance should be based on the latest available report, preferably not more than 30 minutes before the expected landing time.

Do you have some other reference?

regards

[BOAC]

having regard to the performance information contained in the Operations Manual - do you have an Ops manual, haroon and what does it say? Does the Ops manual have any part that is carried on an aircraft detailing LDR for different conditions? Which a/c type are you asking about?

[Haroon]

having regard to the performance information contained in the Operations Manual

To me it seems that while deciding what would be a safe landing, one has to consult the performance information in the ops manual.

do you have an Ops manual, haroon and what does it say? Does the Ops manual have any part that is carried on an aircraft detailing LDR for different conditions?

e.g. B777 - Performance Inflight Section - Normal Config Landing Distance

It has the LDR for different conditions. It also states that the distances are actual and unfactored.

Which a/c type are you asking about?

Not any specific type. Was just interested to know if it is written clearly somewhere that factors need not be applied during inflight re-planning.

The logic of applying the factors is that we need some safety margins, since a normal flight by an average pilot is not flown the same way as a test flight by a test pilot.

The logic seems to be valid whether one is on the ground or in the air. For departure the rules state clearly that it is mandatory. However for inflight re-planning under normal conditions (i.e. no emergency and land ASAP condition) I was interested to see what the rules say.

thanks

[BOAC]

haroon - my understanding (based on UK ops under EUOPS) is that for 'normal' landings, crews must apply the same 15% factor to any 'unfactored' manufacturer (eg QRP/PIFS figures). The only time this is not needed is in an emergency or 'non-normal'.

Two items to view

the CAA information document :
http://www.caa.co.uk/docs/1428/20120801OperationsOnContaminatedRunways.pdf

and a recent thread here on the topic
http://www.pprune.org/tech-log/471353-required-landing-distance-available-does-inflight-requirement-exist.html

[safetypee]

Haroon, there is no specific factor recommended for in-flight assessment. The issue revolves around safety, which as discussed in previous threads places the responsibility with the Commander.
Thus, the judgement of safety (acceptable risk) could involve arguing why a 1.92 factor was deemed safe before takeoff, but not necessary before landing. And as you indicate, it’s better to consider that in-flight rather than off-the-end of a runway.

Use of in-flight data depends on a good understanding of the basis of that data and the assumptions in it. Many manufacturers are revising their ops-manual data; see the threads relating to OLD.
http://www.pprune.org/tech-log/503028-a320-flight-actual-landing-distance.html
http://www.pprune.org/tech-log/498034-new-landing-distance-calculations-airbus.html

Even with improved data, a Commander will still have to consider additional factors; a good guide to these is in AC 91-71 Runway Overrun Prevention. (http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/73552)

BOAC, IIRC the (UK/EU) 15% only relates to contaminated runway operations. There is mounting evidence that this factor is insufficient in the wide range of conditions / reports for this case; and that the landing data may also depend on the presumption that contaminated runway should not be used routinely (avoided) or additional mitigation taken.

[Microburst2002]

Inflight replanning is still planning, ergo all factors apply, including weather minima.

A diversion is another story, though.

[Fullblast]

Haroon, as you noticed ops 1.400 doesn't mention any factor, so you don't have to apply any correction..legally. The word "legally" should not be, in my opinion, over-emphasized because it doesn't mean necessarily "safe". Actually, the regulation gives the responsibility all over the commander as Safetypee correctly says.
Microburst, I agree with you that a re-planning is a planning anyway, but this is irrelevant in this contest. Haroon used the word re-planning, but regulations doesn't, according to them you have only 2 scenarios, before dispatch and in-flight; diversion alternate follow the same rules.

FB

[Fokker-Jock]

Inflight replanning is only applicable if you replan in such a way that you change your original plan with a new destination or new alternate. You therefore have to perform a new dispatch calculation if performing a replanning.

There is no requirement for doing a REPLAN in air if the weather conditions change after takeoff. Only operational calculations apply. No factors, unless your company require you to do so. Regulations doesn't.

Dry regulatory requirements are factored 1.67
Wet regulatory requirements are factored either 1.92 of dry data or 1.15 of wet data whichever is higher.

Contaminated regulatory requirements are either 1.92 of dry data or 1.15 of contaminated data whichever is higher.

With regard to winds you must also perform another calculation based on the most favorable runway in no wind conditions. Should you require a specific wind component to land on the runway most likely to be designated you may dispatch using two alternates satisfying the above criteria.

I could go on and write a lot more, but these are the basics. Need to go now..

Later!

[Microburst2002]

EU OPS 1.515, the one mentioning the 60% rule is not, in my opinion, restricted to planning stage. It is not like the planning minima. The operator has to ensure that pilots land within 60% of the runway. And so OMs usually include such rule, even in flight, while in normal ops.

The commander, not the operator, is obligued by the more generic rule, 1400, to ensure that a safe landing can be made.

So a pilot, if there is no overriding circumstances, has to abide by his OM, that should state the 60& rule except in abnormal operation.

[HazelNuts39]

If the regulators had intended a rigid application of landing distance factors in 1.400, they could have stated that intent explicitly. Since they didn't, the text the drafting committee adopted IMO leaves some discretion to national authorities such as the UK CAA to either lay down specific criteria for operations conducted under their jurisdiction, or to leave the matter to the discretion of the aircraft commander.

[Fokker-Jock]

EU OPS 1.515, the one mentioning the 60% rule is not, in my opinion, restricted to planning stage. It is not like the planning minima. The operator has to ensure that pilots land within 60% of the runway. And so OMs usually include such rule, even in flight, while in normal ops.

A lot of pilots think that as long as you have two alternates you can dispatch to any destination not complying with performance requirements for dispatch. This is wrong. If the airport you are planning to fly to have two or more runways and you cannot perform a dispatch calculation satisfactorily. You are not allowed to dispatch at all towards that airport. Remember that dispatch calculations consider the mass of the aircraft at time of departure, whilst operational calculations consider the LDA vs Landing distance required. This subtle difference actually means something in terms of complying with regulations.



OPS 1.475:
(a) An operator shall ensure that the mass of the aeroplane:
1. at the start of the take-off; or, in the event of in-flight re-planning;
2. at the point from which the revised operational flight plan applies, is not greater than the mass at which the
requirements of the appropriate Subpart can be complied with for the flight to be undertaken, allowing for
expected reductions in mass as the flight proceeds, and for such fuel jettisoning as is provided for in the particular
requirement.

These regulatory requirements in Subpart F (description)/Subpart G (Requirements for Performance Class A) are valid for dispatch of an aircraft.
You may be legally allowed to dispatch towards an airport although you may not necessarily be able to land there from an operational use of the same performance data because your operator may have added margins to the performance test data provided from the manufacturer of the airplane.

In my company operating the 737 the company has in it's OM a requirement to only use "Autobrake Max" values factored by 15% for operational use as a way to determine (or more correctly help the commander determine) whether a safe landing can be made.

HazelNuts39 got it right. The regulatory agency sets forth requirements for dispatch whilst the operator needs to provide an approved method of using the manufacturers performance data for operations.

That's why you need to perform a dispatch calculation before commencing a flight to satisfy regulations, whilst airborne you need to perform an operational calculation before landing to satisfy company regulations (approved by the authority)

In other words, as a Commander in flight you need to satisfy yourself, given all relevant data available to you, you are able to perform a safe landing :) Definition of safe is basically up to you/Operator

Just rememberd with regard to inflight dispatch calculation as asked for in the original post. The only time you need to perform a dispatch calculation in flight is when you have used the exemption rule (Airport having a single runway, where landing depends on a specified wind component. Dispatch can be made with two alternate airports that comply with regulations) A new dispatch calculation must be made satisfactorily in flight. However during this calculation you only need to comply with requirements for the actual runway (Not the most favorable in still wind). REF: OPS 1.515 d)

[Microburst2002]

reading more carefully I see that 1515 is referred to 1475, which is clearly about planning.

And I don't find anything else for non planning stage than the 1400...

[john_tullamarine]

Consider -

(a) the practical rule is "don't crash".

(b) the rule following the mishap is "make sure that you have a good story for the Judge" .. as you are going to live/die in your career etc., on the basis of whatever your decision processes were on the day.

Putting whatever rules may exist and whatever your interpretation of the rules may be to one side ... this leads to

(a) if the operation is planned and has available options and alternatives, then adopting not less than the normal certification fudge factors which have stood the test of time .. just might be a good idea as a routine protocol. The AFM/POH is a useful tool in such circumstances.

(b) if time, fuel, location, and system problems dictate that you have run out of the nice options you would have preferred to have had available .. then you do the best you can in the circumstances .. endeavouring to load the dice in your favour throughout. The QRH/MEL are useful tools in such circumstances.

Of course, the question of why you, as Commander, were in that latter situation may arise subsequently .. but one is better served by being alive and having the opportunity to be able to attempt an answer to the question ..

.. as to the strategy of intentionally squandering those fudge factors in other than emergency or abnormal situations .. where one doesn't have better options ... just doesn't bear thinking about.

[Haroon]

Thankyou everyone for your input:

If I summarise everyone's input (considering that I've understood everyone's point of view correctly), following is the picture so far:

The logic of applying the factors is that we need some safety margins, since a normal flight by an average pilot is not flown the same way as a test flight by a test pilot. If the logic seems to be valid on ground then what makes it invalid in the air?

The judgement of safety could involve arguing why a factor was deemed safe before takeoff, but not necessary before landing.

So first we have to decide whether the safety margins are required during in-flight determination of the landing distance or not. How much is another story.


To start off with JAR-OPS 1.400:

JAR-OPS 1.400 Approach and landing conditions

"Before commencing an approach to land, the commander must satisfy himself that, according to the information available to him, the weather at the aerodrome and the condition of the runway intended to be used should not prevent a safe approach, landing or missed approach, having regard to the performance information contained in the Operations Manual."

If the regulators had intended a rigid application of landing distance factors in 1.400, they could have stated that intent explicitly. Since they didn't, the text the drafting committee adopted, leaves some discretion to national authorities to either lay down specific criteria for operations conducted under their jurisdiction, or to leave the matter to the discretion of the aircraft commander.

The issue revolves around safety.

Is it unsafe to takeoff without safety margins for landing at destination?

Is it safe to land without safety margins in case the surface conditions at the time of landing are different from those planned at departure?

If JAR-OPS 1.400 is about safety then the interpretation of safety by national authorities CAA and FAA is:

1) CAA: Operations on Contaminated Runways
http://www.caa.co.uk/docs/1428/20120801OperationsOnContaminatedRunways.pdf

2) FAA: Landing Performance Assessments at Time of Arrival (SAFO 06012)
http://www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/safo/all_safos/media/2006/safo06012.pdf

Both authorities support in-flight application of safety margins.


In addition to above another reference that provides an indication about in-flight re-planning is:

JAR-OPS 1.475:

General

(a)An operator shall ensure that the mass of the aeroplane:

(1) at the start of the take-off; or, in the event of in-flight replanning

(2) at the point from which the revised operational flight plan applies, is not greater than the mass at which the requirements of the appropriate subpart can be complied with for the flight to be undertaken, allowing for expected reductions in mass as the flight proceeds, and for such fuel jettisoning as is provided for in the particular requirement.

An operator shall ensure that the approved performance data contained in the aeroplane flight manual is used to determine compliance with the requirements of the appropriate subpart, supplemented as necessary with other data acceptable to the Authority as prescribed in the relevant subpart. When applying the factors prescribed in the appro- priate subpart, account may be taken of any operational factors already incorporated in the aeroplane flight manual performance data to avoid double application of factors.
When showing compliance with the requirements of the appropriate subpart, due account shall be taken of aeroplane configuration, environmental conditions and the operation of systems which have an adverse effect on performance.

For performance purposes, a damp runway, other than a grass runway, may be considered to be dry.

An operator shall take account of charting accuracy when assessing compliance with the take-off requirements of the applicable subpart.

Landing — dry runways

(a) An operator shall ensure that the landing mass of the aeroplane determined in accordance with OPS 1.475(a) for the estimated time of landing at the destination aerodrome and at any alternate aerodrome allows a full stop landing from 50 ft above the threshold:

(1) for turbo-jet powered aeroplanes, within 60% of the landing distance available; or

(2) for turbo-propeller powered aeroplanes, within 70% of the landing distance available;


However several operators and many pilots do not interpret “or, in the event of in-flight replanning” as being applicable to planning an approach, as in requiring a reassessment of the conditions for landing. Their point of view is that ‘it only applies to diversion’.

i.e. inflight replanning is only applicable if you replan in such a way that you change your original plan with a new destination or new alternate. You therefore have to perform a new dispatch calculation if performing a replanning. Whilst airborne you need to perform an operational calculation before landing to satisfy company regulations (approved by the authority).

But over all I think everyone agrees that in an event of in-flight assessment/determination/planning or whatever the terminology is, some sort of safety margins need to applied above the actual unfactored landing distance.

If rules can specify precise factors for preflight planning then why cant they do that for inflight planning? IMO may be because inflight planning is much tighter than the preflight one (e.g. you cant offload payload, financial cost of diversions etc), so they've left it up to the national authorities who have left it up to the operators. And those operators who havent specified anything will take take advantage of the wordings in JAR-OPS1.400 "commander must satisfy himself" :}

So moral of the story: "make sure that you have a good story for the Judge"

[9.G]

Haroon, making simple things complicated won't make your life easier. Airbus has introduced operational landing distances containing necessary margins and covering various runway conditions, aircraft status and failures. Make it simple: Say you're flying a long haul for 10 hours after 5 hours upon entering some FIR ATC tells you to divert to the airdrome X, with LDA 9000 ft, due to airspace being closed for whatever reasons. Now your actual landing distance with current GW, as per QRH in the flight performance table, is 7000 ft. If you apply it you can land safely if you think to re-plan then you'd need 11690 ft. No brainer there, if you ask me. :ok:

[Haroon]

Haroon, making simple things complicated won't make your life easier.

What do you have to say about the CAA/FAA safety circulars?

Airbus has introduced operational landing distances containing necessary margins

Boeing has'nt

Say you're flying a long haul for 10 hours after 5 hours upon entering some FIR ATC tells you to divert to the airdrome X, with LDA 9000 ft,

What if they tell you to land at airdrome X, with LDA 7100 ft.

If your actual landing distance as per Boeing QRH (unfactored) is 7000 ft, can you apply it and land safely? :ok:

[9.G]

What do you have to say about the CAA/FAA safety circulars?

TALPA concept was designed based on safety concerns pertaining those circulars. It's an realistic assessment principle independent of the manufacturer. Boeing or airbus can adopt it as they wish. It's not a rule yet.

If your actual landing distance as per Boeing QRH (unfactored) is 7000 ft, can you apply it and land safely? Well, if you believe to able to perform a test landing then do it otherwise you can declare MAYDAY and ask for the ground services to standby as you'll have to land anyway presuming that's the only choice given by ATC, as per Scenario. :ok:

[LYKA]

Maybe my simplistic view. Why can't you dispatch with two destination alternates as long as both of those satisfy the dispatch criteria?

[Fokker-Jock]

Maybe my simplistic view. Why can't you dispatch with two destination alternates as long as both of those satisfy the dispatch criteria?


If your dispatch calculation shows that you cannot land on the most favorable rwy in still winds but you can land on the rwy most likely to be assigned given the forcasted wind/weather conditions you can dispatch with two alternates that comply fully with the dispatch requirements. When doing this you need to perform a new calculation before landing with the latest weather reports available, and satisfy dispatch criteria on the runway assigned to you. If this calculation fail, even though your inflight assessment of a safe landing permits you to land, you are not legally allowed to land on that runway.

However; This exemption rule cannot be used if your destination have more than one runway.

If you can land on the most favorable rwy in still wind but not on the rwy most likely to be assigned given the forcasted weather conditions, you may dispatch with only one alternate complying fully with the dispatch requirements.



OPS 1.515
Landing — Dry runways

(a) An operator shall ensure that the landing mass of the aeroplane determined in accordance with OPS 1.475(a) for the
estimated time of landing at the destination aerodrome and at any alternate aerodrome allows a full stop landing from
50 ft above the threshold:

1. For turbo-jet powered aeroplanes, within 60 % of the landing distance available; or
2. For turbo-propeller powered aeroplanes, within 70 % of the landing distance available;

(b) When showing compliance with subparagraph (a) above, an operator must take account of the following:

1. the altitude at the aerodrome;
2. not more than 50 % of the head-wind component or not less than 150 % of the tailwind component; and
3. the runway slope in the direction of landing if greater than +/-2 %.

(c) When showing compliance with subparagraph (a) above, it must be assumed that:
1. the aeroplane will land on the most favourable runway, in still air; and
2. the aeroplane will land on the runway most likely to be assigned considering the probable wind speed and direction
and the ground handling characteristics of the aeroplane, and considering other conditions such as landing
aids and terrain.

(d) If an operator is unable to comply with subparagraph (c)1 above for a destination aerodrome having a single runway
where a landing depends upon a specified wind component, an aeroplane may be despatched if 2 alternate aerodromes
are designated which permit full compliance with subparagraphs (a), (b) and (c). Before commencing an approach to
land at the destination aerodrome the commander must satisfy himself/herself that a landing can be made in full compliance
with OPS 1.510 and subparagraphs (a) and (b) above.

(e) If an operator is unable to comply with subparagraph (c)2 above for the destination aerodrome, the aeroplane may be
despatched if an alternate aerodrome is designated which permits full compliance with subparagraphs (a), (b) and (c).

[Fokker-Jock]

@Haroon;

I think you've summed it up quite correctly.
You've also added a couple of questions:

Is it unsafe to takeoff without safety margins for landing at destination?

It's not necessarily unsafe to do this as long as the conditions doesn't change enroute, but it's not legal. Definition of safe is not a regulatory issue. The regulatory agency has made the definition of safety up to national agencies/operators/commander to determine. For instance; one operator could get approval for one type of inflight assessment based on their training, type of equipment, experience level etc etc etc, whilst another operator would not.

Is it safe to land without safety margins in case the surface conditions at the time of landing are different from those planned at departure?


Not necessarily either. Not advicable perhaps, but not necessarily unsafe. Again see the answer above. Say your LDA is 7000 ft and your calculated unfactored landing distance is 7000 ft. If you fly your aircraft exactly how the unfactored landing distance was calculated. Vref+0 at 50 ft. Touchdown 305meters down the runway, application of maximum wheelbrakes 1 second after touchdown, deployment of reverse 2 seconds after touchdown up to full reverse down to 60 kts, before using wheelbrakes to come to a complete stop. Your nosewheel should be at the edge of the asphalt at the end of the runway. Certainly not unsafe. You can taxi fat and happy back to the gate, and all passengers are safe and sound without any injury to pax or damage to the aircraft. ARE MOST PILOTS OK WITH THAT ? Certainly not. How much margins you add are up to you, but I would certainly consider; Worn brakes, MEL, long days with fatigue, unreliable weather reports, unreliable friction measurements, worn tyres, increased ref speeds, pilots experience level, light conditions, and on and on and on. How much margins ? If using the dispatch margins you've given yourself a lot of margins. I would even say too much margins since you would have problems even landing at all applying all those factors, but you're not wrong to do so. It's all up to you. You can even add more margins if you deem it necessary.

If rules can specify precise factors for preflight planning then why cant they do that for inflight planning?

What do you mean by inflight planning ? Planning ends when the aircraft is moving under it's own power for the intention of flight. You do your planning on the ground before commencing your flight. If you receive information enroute to your destination that your alternate airport is closed due weather, you need to perform a replanning. A replanning must meet regulatory requirements, hence a dispatch calculation for your new alternate must be successful.
Rules or rulemakers do not specify specific criterias for inflight assessments. They require you to have the methods/SOP you intend to use approved. That's why you sometimes see some operators land and some don't because their approved criterias are different. :ugh:

[Haroon]

thanks Fokker-Jock

[LYKA]

And the same applies for WET and Contaminated RWYs?

[safetypee]

9.G, “No brainer there, if you ask me”.(#17)
A pre landing check / reassessment should be standard practice; this involves conscious thought about the inherent risks.
If the example 7000ft landing distance was based on ‘actual’ tables, it perhaps overlooks the more representative 8600ft, consisting of +600ft realistic airborne distance, +500ft for 10kts fast on a wet runway, and +500ft for 2sec delay in braking, - all normal operational behaviour (AC91-79 data).
The revised distance still requires an adequate level of braking, timely selection and use of reverse thrust, and assumes that the runway braking action and wind are as reported. Without these, where the latter depend on other people, a 9000ft LDA may only give a 5% margin, but with other considerations such as type of runway surface, or exactly how wet the runway might be; no safety margin.
Think about it.

[9.G]

s.t Airbus has introduced operational landing distances containing necessary margins and covering various runway conditions, aircraft status and failures. The assumption was based on the new OLD concept. With the OLD one can also use the physical length of the RWY as sufficient margins, as mentioned by you, are built in. One can exaggerate and picture the end of the world or simply be aware of the assumptions and inherent risks, not excluding incompetence. :ok:

[safetypee]

9.G, I agree that OLD provides a better basis for landing performance, but it is only a basis, which has to be evaluated against the current situation before landing.
It’s not necessarily ‘incompetence’, but the normal variability of human performance, both in flying and judging the risks in a situation. There are good examples of these in the Boeing analysis (http://flightsafety.org/files/ASW_nov12_sm.pdf) - pages 8-13.

In addition to the three main items of aircraft control - touchdown distance, speed, and spoiler / brake application, there is combination of circumstances, such as tailwind and medium / poor braking (Table 1). Also note the distance margin used for the normal (non-long) touchdowns; up to 20-30% of the available distance.

http://www.superstructuregroup.com/Resources/Cathay_Pacific_TEM_Analysis.pdf is a good example of how to manage the threats and risk of error when landing; these aspects still apply even when using OLD.

[LeadSled]

An operator shall ensure that the approved performance data contained in the aeroplane flight manual is used to determine compliance with the requirements of the appropriate subpart
Folks,
The landing field length from the AFM will be certified data, ie; it has been factored. This is the landing field length for all but emergency operations.
Basing any of your operation on "raw" test flight numbers has no place in any commercial operation. Likewise, "tricky" interpretations of rules by bush lawyers has no place.
It is highly unlikely that the average pilot, in the average aeroplane, would even get close to the raw (unfactored) field lengths achieved during certification test flying.
Assuming the above quote is correct, I would have thought that would settle the argument.
Tootle pip!!

PS: FokkerJock,
Is that intended to be a definition of how test flight landing field lengths are established --- it's a new one on me.

[Fokker-Jock]

Hi LeadSled,

No it's not. It is the conditions upon which the advisory performance information in the AFM are based on. For complete definitions of how flight testing data are validated for aircrafts certified under FAA regulations you need to look up FAA AC 25-7A "flight test guide for certification of transport category aircrafts"
or EASA CS-25 for the european norms.

I can only assume that the conditions listed in the AFM are derived from one of the three AMC (Acceptable Means of Compliance) listed in AC 25-7A for determination of Airborne distance.

I was not present during the first B737 certification so this is what I was able to dig up on the subject.
In fact I wasn't even born :)