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MysteriousMrX 01-30-2019 06:02 AM

ACARS vs dispatch release
 
Had a flight the other day (fly CRJ-900) ..
Dispatch paperwork said planned takeoff weight was something like 74,200 lbs. Max takeoff weight 79,000lbs, roughly.
Loaded the numbers into ACARS.. said our weight was about 74.2.. as planned.. however it said our max weight was 74.7 or something like that. Why?
Am I missing something basic here? Let’s say we had extra bags and were overweight? We can’t go. But what if ACARS is in-op and we do paper w/b.. we could be several THOUSANS pounds over and be ok according to the release, right?!

Other question, re: required landing length.
We need a certain length to stop the aircraft, but we add 60% to be legal and safe. ACARS will say our min length is, let’s say 3000’ but 4800’ is the required. SO, if you if you get let’s say, a Spoileron fail caution or whatever, you add 20% to the landing distance. Is that 20% of the lower or higher number? (Read an ASAP where a crew couldn’t land in SBA because adding the 20% put them at needing more runway length than was available; they diverted)
If ACARS is in-op, we use the dispatch release which only has the distances with the 60% added already, correct? So if we had to add 20% do we add it to the release’s numbers? Or figure out what the min landing length is off that number and add 20% to that?

Airbum 01-30-2019 06:15 AM

. At my company your questions most likely answer is that AERO data calculated the max allowed take off weight based on the current conditions you input into the program for your planned take off. Reference your Performance data section of your Aircraft Operating Manual. You can change the inputs into AERO data to increase your allowed max take off weight ie: use max thrust, change flap setting, change runway.

ACARS is a communication and data link system. At my company it does not do performance data or weight and balance problems.

We use AERO data which is a performance data program for dispatch in which we receive the information over the ACARS. AERO data program is also used for actual landing performance data while airborne.

AERO data takes MEL performance limitations and applies them to your landing data solution. For both dispatch and actual landing performance calculations

sigler 01-30-2019 07:39 AM


Originally Posted by MysteriousMrX (Post 2752662)
Had a flight the other day (fly CRJ-900) ..

Other question, re: required landing length.
We need a certain length to stop the aircraft, but we add 60% to be legal and safe. ACARS will say our min length is, let’s say 3000’ but 4800’ is the required. SO, if you if you get let’s say, a Spoileron fail caution or whatever, you add 20% to the landing distance. Is that 20% of the lower or higher number? (Read an ASAP where a crew couldn’t land in SBA because adding the 20% put them at needing more runway length than was available; they diverted)
If ACARS is in-op, we use the dispatch release which only has the distances with the 60% added already, correct? So if we had to add 20% do we add it to the release’s numbers? Or figure out what the min landing length is off that number and add 20% to that?


I’m not sure I got your question correctly, but I as far as I understand, landing within 60% of the runway is for dispatch purposes only. Once you’re airborne, you use whatever your company provides for calculating your in-flight landig distance, with the actual conditions at the time including any failuers you may have had enroute. In addition to the company-provided software you may have on board, the QRH should have a section for calculating in-flight landing distances with failures.

Twin Wasp 01-30-2019 09:41 AM

Did you compare the data the release was based on versus the numbers you imputed to get your numbers? Was there a change in runways, runway condition, temperature or wind? Did your numbers tell you what the limiting factor was, runway or climb performance? Did you call your dispatcher and ask about the difference?

121.195 says you can not depart to an airport unless at the planned landing weight you are able to stop within 60% of the landing distance available (not add 60%.) To make the math easy, if the performance date says you need 6000 feet to land, the runway you plan to land on must be 10,000 feet. Once you takeoff that goes out the window. Say your destination airport has two parallel runways, 10,000 and 7500 feet long. You can land on the shorter runway because you only need 6000 feet to stop. If you have an issue enroute and your procedure requires you to add a performance penalty you would add it to the 6000 landing distance.

As pointed out above your QRH should have some performance in flight tables to get an idea what your landing distance will be. And some airlines use an onboard computer to figure performance so it doesn't matter if ACARS is inop.

The FAA has been pushing manufacturers and airlines to use factored landing data which has an additional 15% added. So if the manufacturer determined that your aircraft with a given set of conditions needed 5000 feet to come to a stop the tables would say you 5750 to come to a stop.

MysteriousMrX 01-30-2019 10:33 AM

Thx for the responses. I may be overthinking some of it..
I’ll try putting in the exact weather conditions in the ACARS next time and see what it gives- just seemed odd it was so far off compared to the release.

Ok I worded the 60% thing wrong. I think.
So when ACARS says unfactored distance is 2968 and minimum required is 4312 (estimating numbers here) .. it just means I can stop the aircraft in 2968’. But we’re saying 4312 to be safe so the runway needs to be a length that is equal to 7186 (4312 is 60% of 7186)

So now let’s say we have to add 20% to our length for some QRH reason. .. I’m a multiplying 2868 by 20% or 4312?

Now ACARS is out. Using the release. It says my min req’d landing for the conditions that exist is, let’s say 4455’ (ACARS usually gives shorter lengths). Same Qrh scenario. I’m adding 20% to that number?

sigler 01-30-2019 11:41 AM


Originally Posted by MysteriousMrX (Post 2752866)
Thx for the responses. I may be overthinking some of it..
I’ll try putting in the exact weather conditions in the ACARS next time and see what it gives- just seemed odd it was so far off compared to the release.

Ok I worded the 60% thing wrong. I think.
So when ACARS says unfactored distance is 2968 and minimum required is 4312 (estimating numbers here) .. it just means I can stop the aircraft in 2968’. But we’re saying 4312 to be safe so the runway needs to be a length that is equal to 7186 (4312 is 60% of 7186)

So now let’s say we have to add 20% to our length for some QRH reason. .. I’m a multiplying 2868 by 20% or 4312?

Now ACARS is out. Using the release. It says my min req’d landing for the conditions that exist is, let’s say 4455’ (ACARS usually gives shorter lengths). Same Qrh scenario. I’m adding 20% to that number?

Are you asking about a failure before take off, as in the airplane is dispatched with a MEL item that affects landing performance? If so, multiply your total RLD (4312’ in your example) by whatever factor your MEL tells you to. Once in flight, or if you have a failure in flight, use whatever means your company gives you to calculate your in-flight landing distance, or the QRH. Forget about the numbers on your release, they no longer apply once you’re airborne.

MysteriousMrX 01-30-2019 05:46 PM


Originally Posted by sigler (Post 2752916)
Are you asking about a failure before take off, as in the airplane is dispatched with a MEL item that affects landing performance? If so, multiply your total RLD (4312’ in your example) by whatever factor your MEL tells you to. Once in flight, or if you have a failure in flight, use whatever means your company gives you to calculate your in-flight landing distance, or the QRH. Forget about the numbers on your release, they no longer apply once you’re airborne.

No.. no MEL. we’re in flight. All is good. ACARS says runway is 8500’ long, so I guess we need 5100’ to stop. But given our weight, winds, etc.. it says we can conceivable stop in 3500’. Now we’re descending and we get a caution message and run the QRH. It says add 20% to the landing distance. Am I adding 20% to 3500 or 5100? (I know either way I can land.. but I want to be right about this)

Question 2: same scenario but ACARS went no-comm and I’m relying on the release. It says dry runway at this weight requires 5250, let’s say. Do I add 20% to that? If that’s the case then I should be adding 20% to the higher number w/ ACARS, right?

2StgTurbine 01-30-2019 06:38 PM

This stuff should have been covered in indoc. I suggest you write an ASAP so your airline's training department will include this in their training program.

MysteriousMrX 01-31-2019 05:19 AM


Originally Posted by 2StgTurbine (Post 2753245)
This stuff should have been covered in indoc. I suggest you write an ASAP so your airline's training department will include this in their training program.

k.. and the answer is? or you don’t know?

sigler 01-31-2019 05:35 AM


Originally Posted by MysteriousMrX (Post 2753206)
No.. no MEL. we’re in flight. All is good. ACARS says runway is 8500’ long, so I guess we need 5100’ to stop. But given our weight, winds, etc.. it says we can conceivable stop in 3500’. Now we’re descending and we get a caution message and run the QRH. It says add 20% to the landing distance. Am I adding 20% to 3500 or 5100? (I know either way I can land.. but I want to be right about this)

Question 2: same scenario but ACARS went no-comm and I’m relying on the release. It says dry runway at this weight requires 5250, let’s say. Do I add 20% to that? If that’s the case then I should be adding 20% to the higher number w/ ACARS, right?

Once you’re in flight, you no longer use the numbers on your release. I am not sure what method your company uses for figuring out in-flight performance calculations (mine uses Airbus’ FlySmart on ipads), but regardless of what it is, it will be derived from the same source the QRH uses. So you can always rely on the QRH. There should be a section for landing distances with failures in there somewhere. If there isn’t, you just use the regular landing distance section and multiply whatever result you get by the factor listed for that particular failure, and then by 1.15.


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