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?

. 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

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.

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.

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.

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?

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?

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.

Ok.... so again, we’ll assume ACARS works. It says we need 3500’ to stop it, 5100 for the 60% of the runway number. Which of those do we add the 20% to?! Let’s start with that to un-confuse me.

The reason your questions are so hard to answer is you are getting numerous performance topics confused.

The 60% rule is for DISPATCH only. Before you depart, the dispatcher makes sure that there is at least one usable runway that you can land WITHIN 60% of (you divide your actual landing distance by 0.60).

But once you get in the air, that number no longer matters. The dispatcher was using forecasted conditions. You as a pilot have more information. You have the current ATIS and braking action reports. Because you have more accurate information than the dispatcher did hours before when they made the release, the FAA does not require you to have a 67% safety margin (remember that the DISPATCH rule was to land WITHIN 60%) that's over the actual landing distance; they require only a 15% margin. That is what the ACARS number should be giving (but since I am not at your airline I have no idea what your company is using for performance). I have never worked at an airline that gave ACARS landing data with the 60% dispatching rule.

Another important thing to consider is the assumptions based in the performance calculations. Your company may differ from the ones I worked at, but usually the dispatcher assumes you are landing the plane like a test pilot. You cross the threshold at Vref and touch down with minimal flare/no floating a few knots below Vref. Then you apply max wheel braking with no reverse thrust credit. Since no one actually lands like that, the landing performance you get through ACARS normally has more realistic assumptions or allows you to select reverse thrust credit, braking level, wind additives to your approach speed, etc.

Now when it comes to QRH landing data (again your airline may differ), those corrections are normally based on the ACTUAL landing data (that 60% rule is only for your release). Some airlines have a separate performance manual for abnormal situations. The numbers in those usually include a safety margin in the numbers already.

As you can see to answer your questions, I had to make a lot of assumptions about your airline, so therefore, my answers may not be very helpful. That is why I told you to write an ASAP so your company can fix this. All this information should be in your FOM, the manual your dispatchers use, or in a section of the QRH where it teaches you how to use that manual.

The advice you've received so far is as accurate as can be with what is known;

I'll add a few of my thoughts which hopefully add to the discussion:

The 79,000 LB number looks like a nice round number that could be the manufacturer's max structural takeoff weight. A "never exceed" weight that has nothing due to performance calculations. Just an upper limit.

In other words, a CRJ-900 departing a 15,000 foot runway on a cold dry day flying a fairly long segment in flat terrain might be able to weigh that amount.

Many times that max structural weight for takeoff is never reachable because of other factors. They usually include:

DEPARTURE
EN ROUTE
LANDING

Let me expand on these:

departure - limits due to the departure runway TORA, TODA, ASDA, and then climb limits due to surrounding terrain upon departure, based on takeoff power/thrust setting, LE/TE device setting, ambient conditions, and other factors like anti-skid, auto-spoiler, auto-brakes (insert whatever equipment that matters here)

en route - limits due to terrain clearance during the flight to meet driftdown performance when OEI (only certain parts of the world that have tall-enough mountains where it matters)

landing - a weight that includes destination/alternate runway limiting weights based on the -900's performance for the approach & landing;
stopping on the pavement - LDA
OEI approach climb (missed)
all-engine landing climb (go-around)
you must ADD your planned fuel burn to get you there.

quick example: Peoria to O'Hare you might burn what, 1000 lb?
If your max landing weight for ORD runways are 73,500 lb, you can't weigh more than 74,500 in Peoria, even if you have a long runway, it's cold, etc - you cannot plan to land overweight. The 79,000 lb number doesn't apply.


These weights are calculated for planning purposes at release time and the LOWEST (most limiting) of the 3 is what will be your "max takeoff weight" for that leg.

My educated guess is you saw the 79,000 lb limit, compared it to your actual weight of 74,200 -but that doesn't tell the whole story.

The 74,700 lb number is likely the "more correct" limit.

I'm not familiar enough with the -900, so perhaps a "flex" thrust setting that was still good enough for your airplanes current load was part of that "more correct" limit calculation. If more bags/people/support animals/whatever showed up, you would likely get a new limiting takeoff weight calculated (remove the flex, use max thrust, flap 8 instead of 20, different/longer runway, etc) to give you the elbow room for the new airplane weight.

Many/most operators use a reduced thrust/power for takeoff for engine longevity, perhaps a flap setting that allows for lower tire speeds, when the people/cargo that show up isn't a large number. Maybe this is why it looked to you why you "were really close" to going overweight when really you had more wiggle room.

They do this to reduce wear & tear, etc. When the weights are higher, you do the very best the book will allow.

Hopefully you see that Bombardier's max structural takeoff weight, max structural landing weight, which are sometimes "salesperson" numbers - quickly become meaningless in this context.

Sorry for wall of text, I hope this helps.

As alluded to above, this could also be an issue of being confused by max flight planned take-off weight vs max runway takeoff weight.

again, I think I’m overthinking it and confusing myself! But thanks for the responses.
The max weight may indeed be something to do with the runway but it was DFW and all runways are very long.

But on ACARS landing data, surely everyone gets the same info: which includes the unfactored length and the longer 60% factored length. As perplexed as others are as to why i don’t know this, I’m equally perplexed no one can answer it either?! Do we add the 20% to the bigger or smaller number?!

If ACARS is no-comm.. I guess we could take the landing distance for our weight off the speed cards. That number will be less than the release numbers that include the 60%. HOWEVER, once again do we add the 20% penalty for whatever QRH procedure requires it to the smaller or bigger? .. now let’s say it’s a snowy icy nasty day. Release says we need way longer distance to stop, right? And now we have QRH saying to add 20% .. adding it to the smaller number doesn’t do anything. So I guess we always add to bigger number??

Your questions have been answered. I will try to simply it. Once you take off, the 60% rule does not matter, that number is only used to plan the flight.

When it comes to QRH corrections, that depends on your airline's specific procedures. Odds are your airline has this in writing in one of your manuals. If you cannot find it, call one of your OE training captains or email your training department since no one on here knows what airline you are talking about.

I will give it one last shot- once you’ve departed, there is no smaller number and big number. Those do not apply anymore. Throw them away. Forget about them. There’s only one number, which is your in-flight landing distance (your company may call it something else). One number, one distance, based on actual conditions, that will be the reference to which you add any factors you may have due to failures.

Ok. So why ACARS gives two, I’ll ask the training department.
But with no ACARS, using speed cards only, we only have that number. Isn’t that based on dry perfect conditions? What if it’s snowy and slushy and crappy? And then we need an extra 20% for whatever QRH scenario happened.

I guess what brought all this to mind was the recent “runway excursions” by Southwest and Mesa and Skywest, and how maybe some things weren’t calculated right.

As pointed out above, without knowing what type of aircraft you are talking about it's hard to give answers. Looking at my Boeing QRH there are landing distance tables for the two approved landing flap settings. Each of those tables has 5 sections for different runway conditions. Each of those sections are further divided to account for 6 different brake settings. There are then another 25 tables to cover various system malfunctions. All of these tables, normal and non-normal, have corrections for altitude, temperature, runway slope, wind and reverse thrust. I would think most manufacturers provide the same information if it applies to their aircraft.

Airplane manufacturers generally provide two distinct Landing data sets: Certified data and Advisory data.
Certified data provides landing distances as required by regulations (FAR parts 25 and 121). Its sole use is to determine landing distance requirements prior to dispatch. As stated earlier, this demonstrated landing distance is determined during flight testing. The demonstrated landing distance parameters are: 50' TCH at VREF, 1000' touchdown, max manual braking, and no reverse thrust.
The Certified FAR Dry distance is 1.67 times the demonstrated landing distance. The Certified FAR Wet/Slippery distance is 1.15 times the FAR Dry distance. But again, this only applies prior to dispatch.
Advisory data provides landing distance capability for different runway conditions and braking configurations. It meets JAR OPS and FAR requirements, as well as SAFO 06012 and TALPA ARC. Advisory landing data is used to determine landing distance to make operational decisions.
SAFO 06012 was a direct result of the Southwest accident at Midway. Prior to the TALPA ARC recommendations, the advisory landing data provided assumed the same as the demonstrated landing distance flown during testing, 1000' touchdown, and no safety margin additive.
The TALPA ARC recommendations were to add a 15% safety addictive to the advisory landing distances, and a more realistic touchdown (1500'). It is also now required to accomplish landing distance assessment prior to arrival.
As such, the normal landing distances in the (Boeing) QRH now include the 15% safety margin and assume touchdown at 1500' (7 second flare distance). Note the non-normal landing distances do not include a 15% additive.
To accomplish the required landing assessment, use the QRH advisory landing distances to compare the applicable landing distances from the QRH against the runway LDA (landing distance available). At a minimum, the max manual braking landing distance must be less than the runway LDA to land. No additional factor needs to be applied.

First, the fact that DFWs runways are "very long" doesn't automatically mean your MTOGW for takeoff on a particular runway, on a particular day is going to be the max certified weight for your aircraft. Factors such as winds, temperature, assumed/flex temps, 10/20 % derated thrust for some aircraft, obstacles, flap settings, etc. may not allow takeoff at max certified weight.

Second, each airline has specific methods they use to compute performance. Mine doesn't use ACARs. We use a program incorporated into our EFB and compute all the data ourselves, both for takeoff and landing. My previous aircraft at the same company used quick reference data in the QRH for landing distance.

Third, information received from whatever source(s) an airline uses may be presented very differently. Assuming we all can decipher the end product you receive and help you with your questions is a big assumption. Along those same lines, your assumption that "everyone" gets the same information when computing landing distance isn't valid. On my a/c, we input landing weight, ATIS information and runway condition, max or idle reverse, MELs/CDLs. The output is landing distance for each autobrake setting and XW/TW components. We don't get unfactored blah blah.... 60% factored whatever and start doing math. It's one number for a particular set of conditions and autobrake setting.

I think the recommendations that you contact your training/standards department are a good start. Having a solid working knowledge of the performance information provided to you by whatever method you use is pretty important when you start getting close to the edges of the envelope dealing with windshear precautions, cluttered takeoffs, runway shortening and obviously landing under less than optimal conditions.

Not so fast, some operators require the factored distance for actual landings.

Yes but the factored distance isn't the "stop within 60% of the LDA" used to release the aircraft.

Your structural max takeoff weight is 84,500. The 79,000 is probably max landing weight plus fuel burn. Was your fuel burn about 3,900? If you took off at a higher weight, you would be overweight for landing. The 74.7 is probably based on a FLX temp (although flaps 8 vs 20 could be an additional factor). If you were to select NO FLEX, AeroData (ACARS) would probably come back with a higher weight. Entering a higher weight would also likely give you good data with a resultant increase in take off N1 (Lower flex temp or even full thrust)

What might be causing some confusion is that there are several different takeoff weights listed in different places throughout a release:

Max structural: 84500 for CRJ 900
Manufacturers performance baseline (my term): often several thousand pounds higher than even max structural
Max flight plan: The most you can takeoff with (considering planned fuel load and burn) and not exceed other weight limitations (usually landing weight, but I'm sure a scenario containing ramp weight or ZFW could be created)
Planned takeoff: Usually right at your planned weight, often with an extra line for 1000/2000# over that. This is where you get your numbers for takeoff if your ACARS is inop.

All of these will make some reference to MAX, TAKEOFF, and WEIGHT, but they are not the same.

In your initial scenario, it is possible that 79,000 was your max flight plan takeoff weight (for max landing weight) and 74.7 was your planned takeoff weight. Maybe there was another line for plus 1000#. Even if there wasn't, you could call dispatch and have them send you a new release with higher numbers.

Again, this is a situation that requires attention to detail. Your QRH most likely references Actual Landing Distance. In that case you would determine Actual Landing Distance (probably from your speed book) and add the 20%. Minimum Landing Distance is a different number (without looking it up, I believe it is a factored number used for dispatch legalities). However, some airlines also require you use a Minimum Field Length number to land (ie, you can't use Actual Landing Distance for normal operations). Using the QRH waives that requirement in most cases.

Best advice: Read the related sections (Performance/Release/Loading/Etc) of your GOM/FOM and your POH/FCOM. Read the QRH items in question. Read them all in detail. Small words make big differences. Also might not hurt to ask other pilots. Like has been said previously, this should have been covered in initial. It will definitely be covered in the upgrade oral/KV.

If any YV Pilots here can access ASAP report from last September re: a flight to SBA that diverted because of a 20% penalty per QRH and the unsuing argument with dispatch as to whether they could have landed.... that’d help clarify things I think.
I’ve asked 2 check airmen, gotten 2 different answers.