Can anyone explain why in the PI QRH the NN landing distances are - Actual (unfactored) distances are shown.

 

Why are they unfactored?

How do we find the factored distances ? - Multiply un-factored landing distance by 1.67 to get factored landing distance? Or is the unfactored without full manual braking and auto speedbrakes?

 

 

Why are they unfactored?

 

The factoring is a dispatch requirement. You're not being dispatched once you're in flight. You might not be heading to an airport you were dispatched to, if you're running the NN.

Hi matt i just got a good answer to it

 

the event of a failure, you do not need a 60% margin, and it would be actually unsafe to require one, as in some cases the extra distance induced by the failure, multiplied by the normal 1.67 factor, would greatly limit the choice of landing sites.

 

So instead a crew are told the true distance for a failure, and expected to apply airmanship in judging how much margin over the absolute minimum they should have, given the failure and any other circumstances. Obviously it is prudent to have some margin.

Like Matt said, factoring is for dispatch. None of that is required once airborne. Plus, remember that in a lot of cases, those non-normal distances are just a best computed estimate - they haven't actually been tested and determined in reality.

Yes of course its only for dispatch and performance inflight data should be used to see if you can still land at your planned destination.

 

But you miss to see my actual question andrew, i was asking why the QRH non normal landing distances are unfactored.

Yes of course its only for dispatch and performance inflight data should be used to see if you can still land at your planned destination.

 

But you miss to see my actual question andrew, i was asking why the QRH non normal landing distances are unfactored.

 

Let's think about fuel for a moment: You have actual fuel burn for A to B and you add your alternate to C and reserve to that to get your Required fuel. That's what you dispatch with, your Required fuel.

 

Now things have gone kablooey and you need to land somewhere with your remaining fuel. It's an emergency.

 

Back to the runway stuff: It's an emergency. Can I land on point A and stop by point B? We don't care about  "reserve" runway.

^^^ yup that. I guess I'm not understanding why you're surprised these distances are unfactored? Why would you expect them to be factored? Normal, dry runway landing data pulled in-flight is also unfactored, at least here in the states. We use factored landing data for a contaminated runway now, but it's a relatively recent development (for some operators anyway) since an accident at Chicago Midway where a Southwest 737 slid off the end of a snow covered runway and struck a vehicle on the road.

 

As I understand it, factoring of runway performance data is done in two circumstances:

1. When there's uncertainty about actual conditions.

2. During dispatch, to account for the possibility of worse than forecast conditions upon arrival.

Can anyone explain why in the PI QRH the NN landing distances are - Actual (unfactored) distances are shown.

 

Why are they unfactored?

 

Hi Vernon!

 

With regards to said operator in the event we have to use the NN Landing distances in the QRH PI (Performance In Flight) which are unfactored and assumes max manual braking and max reverse thrust when available on all, or if one engine INOP, the remaining engine)

 

We use the table to find Reference Distance/Landing Distance regarding the non-normal.

 

Our operator specific policy for using un-factored landing distances is then to.

 

1 - Multiply the distance by 1.3

2 - Irrespective of the figure derived by multiplying the un-factored landing distance by 1.3, our company specifies a minimum LDA of 1900m for non-normal operations

3 - Commander can opt to land using x1.3 factored distance if there is no alternative airports available over 1900m.

 

As everyone else has already mentioned, the x1.67 is a Dispatch Landing distance requirement. The x1.3 is our in-flight operational Landing Distance Data for non-normals

Thats great stuff sam! I have that said operator QRH and from now on i'll apply the x1.3 factor to the unfactored reference distance on the non normal landing part.

 

Will keep those 3 points in mind above

 

Also can you answer why it mentions the DRY figures in the QRH PI are unfactored? but only the WET figures are factored by 1.15

Also can you answer why it mentions the DRY figures in the QRH PI are unfactored? but only the WET figures are factored by 1.15

 

In a nutshell this is In-Flight Landing Performance Data

 

We have three runway states with the applicable tables in the QRH.

 

The Normal Configuration Landing Distances have

 

1. Dry Runway figures which is unfactored, they give the absolute LD, select applicable Autrobrake Setting from table.

2. Wet Runway figures (Good Reported Braking Action) factored by 1.15, select applicable Autrobrake Setting from table.

3. Slippery Runway figures (Medium/Poor Reported Braking Action) factored by 1.15, select applicable Autrobrake Setting table.

 

The Non-Normal Configuration Landing Distances are all unfactored as they all assume max manual braking and max reverse thrust, they have specific tables based on the reported braking action.

 

To answer your question you’ll notice at the top of all the tables in the QRH regarding the in-flight performance data the words ADVISORY INFORMATION which is exactly what this is. Boeing have derived these figures from extensive in-flight testing during the development of the aircraft. They’ve either done it or plugged the numbers into a computer to get these figures.

 

All the landing data presumes prompt application of brakes, reverse thrust and all stopping devices for these figures to be accurate, don’t try and grease her in otherwise you can throw these figures out the window!

 

The Dry figures are unfactored as you can reasonably expect to get the stopping performance quoted in the table, the antiskid has the ability to use most if not all the hydraulic pressure to stop the aircraft on a dry runway with a good braking action.

 

With a Wet/Slippery runway the antiskid system will have to constantly adjust hydraulic pressure to the brakes to prevent the tyres from skidding. Just like the ABS in your car working on a wet/icy road your ability to decelerate will increase so a factor of 1.15 is included to allow for some loss of braking capability.

 

It can seem confusing because All Non-Normal figures are unfactored, this is because max-manual braking is presumed and the decrease in performance with worsening runway conditions is catered for in each specific runway state table.

 

Hope this is helped!

 

 

 

Brilliant sam clears my troubles up on my document that i have which mentions the QRH PI dry distances are unfactored