# How are Landing Distances calculated

#1

How are landing distances calculated in the game? I am trying to setup shop in SNA (with a short runway) and the aircraft performance page is saying that I’m payload limited for the return flight by almost 50% less than the outbound (50% versus 80% total payload). Considering that the aircraft will be essentially empty of fuel on the return, I don’t understand why I wouldn’t be able to carry approximately the same payload back into the airport.

In real life, the landing weight would be calculated using:

Zero Fuel Weight + Payload + Expected Fuel on Board = Landing Weight

Considering the aircraft can take off with 80% payload (and this should include stopping distance should an abort occur at high speed), I find it very doubtful that the aircraft can’t land at anything less than about 80% payload. As far as I can tell, SNA does not have a displaced threshold simulated as that would be the most obvious answer.

FYI- I fully understand aircraft payload, aerodynamics, alternates, and other criteria that enter into this stuff in the real world, but this is not the real world.

This is regarding Quimby using A320 light/ mediums.

Thanks!

EDIT: To be clear, I don’t understand the difference between the stated minimum and maximum landing distances in the game. My guess is that the game uses a linear relationship between the maximum and minimum landing distances and then determines where the actual runway distance falls on that line. Wherever the actual runway distance is on that line, the percentage of payload is calculated. And it doesn’t look at actual or expected landing weight for the calculation. Is landing weight even considered?

#2

While your general question seems justified, let me just correct this:Ä

Operating Empty Weight + Payload = Zero Fuel Fuel Weight

ZFW+Blockfuel-Taxifuel = Take-Off Weight

TOW-Trip Fuel = Landing Weight

Having calculated loadsheets for a living for 3 years, that’s how it’s done.

#3

What you said is correct and I clearly misstated the ZFW as Operating Empty Weight. However, the rest is exactly the same. It is just rearranging what I said above. You simply just expanded the process of determining the expected fuel on board for landing.

Thanks for response and for adding clarity to the ZFW/ OEW miss use. I do appreciate it as they do mean different things.

#4

Close to linear. Every aircraft type has its own runway performance Chart. There is no formula to calculate this type of performance.

Is the actual runway at least as long as the required runway at Max Landing Weight? -> full payload capabilities
Is the acutal runway shorter than the minimum runway requirements (Basically OEW)? -> no flight possible
Linear calculation of the payload capabilities in all other cases. -> As all the specific weights are the same for every route of an aircraft of a specific subtype - the minimum fuel remaining is always the same, so is the OEW.

So there are no landing weight calculations necessary…

This. I think that everyone in the AS teams understands that calculating the runway performance is important in the real world, but this is not the real world. Eyballing these numbers is more than adequate.

#5

Thank you for the reply, but it doesn’t really address what I am referring to. Let me try and state it differently.

First, I know what you stated above as I do this for a living as well. I know for a fact that required takeoff distances are higher than than landing distance at any given weight when dealing with transport category aircraft due to the possibility of a high speed aborted takeoff.

Because landings don’t require the distance to accelerate to a high speed only to then stop (accelerate-stop distance), landing distances are inherently shorter than takeoff distances at any given weight. Thus, you can always bring in more weight INTO a short runway than the takeoff out of it unless you have environmental factors that prevent it. (Prevailing tailwind, unfavorable runway slope, surface contamination, terrain, displaced thresholds, etc.)

AS does not model this correctly. Perhaps their calculations are incorrect, or their baseline values are incorrect- but something is clearly inaccurate. There is no way the max landing distance can be LONGER than their max takeoff distance. Just the maximum landing weight versus the maximum takeoff weight relationship alone would make them very different.

To illustrate, let me state some numbers from Quimby regarding the Airbus 320-200 Lights:

Minimum Takeoff Distance: 1590 M
Maximum Takeoff Distance: 1960 M
Minimum Landing Distance: 1490 M
Maximum Landing Distance: 1990 M

Note: The maximum landing distance is 30 meters longer than the takeoff distance.

I am looking at SNA, though I am not certain other airports with short runways are affected by these inaccuracies. The runway length at SNA is 1737 meters long.

This means that the A320 can take off with nearly an 80% payload and all of the gas to fly to Salt Lake City. However, on the return flight, it can only land with 48% payload in SNA after USING essentially all of the gas during the flight. The aircraft is significantly lighter weight when landing at SNA than when taking off, yet it is saying that the landing distance is much longer, thus requiring to remove payload.

This was for a short flight. Let’s look at SNA- ATL. This flight is over 3,000 kms long and requires a lot more fuel. Again, the A320 is limited on takeoff to 72% payload. This makes sense as it must carry more fuel to fly to ATL and thus the payload is reduced to keep the entire aircraft below the Max Runway Takeoff Weight. However, yet again, the aircraft is restricted to 48% payload for the return flight, even though yet again, the fuel tanks are essentially empty upon landing.

These takeoff payload limitations appear fairly accurate and make sense to me. The landing calculations are way off. As I have done more research and have spent more time on this, to me it is becoming clear that the baseline numbers are incorrect for the A320. The -200 Mediums are similarly affect.

I wholeheartedly agree that eyeballing numbers is good. However, these landing distances are still way off and severely limits the strategies that can be used in the game. The game touts itself as being a realistic representation of reality, and it has a lot of realistic things in it, but this is a glaring fault.

#6

The Airbus A320 (at the edge of its capabilities) needs at a 1750m runway ~1050m from touchdown to full stop. and another 700m are there as a buffer (long landing in bad weather etc.)

V1 is a variable number. There has to be enough distance remaining to bring the aircraft to a stop, but as V1 is below (or is equal to) Vr the aircraft is still on the ground and ready to be stopped.

OK, so SNA-ATL, ~1620nm

from Airbus:

Takeoff:

MTOW is around 74t (ISA conditions) in the real world, so it could start at MTOW - AS performs worse than the real world here

Landing Field Length:

So in the real world Max Landing Weight (once again at ISA conditions) is ~58t, OEW is at ~43t, so roughly 15t maximum payload. This is about as off as the takeoff distance.

You can see the factor of 0.6 has to be applied to calculate the actual landing roll.

see the chart for the actual landing distances:

#7

I have reviewed this multiple times and I am not entirely sure the purpose of explaining all of this. Are you attempting to explain how a landing distance can be longer than a takeoff distance? I feel that you are arguing against my point, but it’s not clear to me. I guess that I’m not understanding the purpose of your response.

For the record, I know that V1 is variable. As I’m sure that you are aware, it also, by definition, means thats that should an engine fail at V1, there will be enough runway to continue to accelerate (slower of course because of only one motor working) to rotation speed, and then be able to clear the obstacle at the end of the runway. This means that V1 will always be near to rotation speed as the airplane doesn’t accelerate or climb as well on only one motor and it would take too much distance for the airplane to accelerate a large amount of speed to get from V1 to Vr. This is true 95% of the time, except where braking action is very low (snow, standing water, ice covered runways, etc). In these rare cases, the V1 will typically be much lower than Vr because the aircraft will need more distance to stop, yet it can accelerate relatively normally.

I also know that a 75 ton airplane will take a significant longer distance to stop than a 50 ton airplane. Setting aside the physical ramifications of inertia and momentum, the true airspeed and thus ground speed required to fly would be significantly higher for a heavier aircraft, thus causing significant distance increases for the heavier airplane due to the higher associated speeds. These facts continue to prove my point that a heavily loaded aircraft will require significantly longer runway distances for takeoff than a lighter aircraft would for landing. I can continue to state the differences between takeoff and landing configurations to further prove the differences in speeds for takeoffs and landings, but for the sake of simplicity and ease, I won’t.

Furthermore, I feel that your landing distance charts even further prove my point.

When it comes to landing on a short field, airlines need to weigh the desire to save on brake maintenance versus doing the route; and 9 times out of 10, they will choose to carry a bunch more revenue (passengers and cargo) and then replace the brakes slightly more often. This means, that they will utilize maximum braking numbers for landing calculations when choosing to operate at short fields. Using this logic, and your posted landing distance calculations, the A320 can in fact use essentially a full landing weight and still have the safety margin required. No airline will voluntarily leave 50% payload behind because they don’t want to use max brakes.

EDIT: To reiterate, my point is very simple. The landing distance values are too long in AS and the maximum landing distance should not be longer than the maximum takeoff distance. I feel that we are getting too much into performance and away from the original purpose.

#8

Also, for the sake of clarity, in your landing field length example, you were basing it off of a field elevation of 8,000 feet. I am unsure whether AS incorporates airport elevation in their distance calculations, but either way, SNA is at sea level.

#9

In fact I was using an elevation of 10000 ft.
Here’s the updated version:

MLW is the green line. So Max landing distance should be ~1490m…

So You are right. A320 landing distance seems off to me too.

It’s all about performance. We don’t calculate these numbers. We are transferring them from the performance charts into tables for AS. And sometimes the landing distances are longer than the takeoff distances. Observed on light (short) variants with relatively powerful engines.

example:

737-700

takeoff field length
1120m at 45t TOW
1320m at 60t TOW

landing field length
1180m at 45t LW
1490m at 60t LW

#10

First off, I haven’t yet thanked you for taking to the time to discuss this. I sincerely appreciate it and I wanted to make sure that I said that.

Yes, this is what queued me into the issue and has brought to light additional issues that I didn’t see before. Considering the fact that 99% of the airports that players use have long runways, this is almost never an issue. However, in the real world, there are several prolific and popular airports that have short runways that have fully loaded, medium sized airliners landing at without any issues. SNA is one example. An other that comes to mind is Chicago Midway (MDW). I live and fly in the USA, so forgive my ignorance for the many other airports with short runways with large amounts of daily operations. (I know LCY is one, but I am not aware of small narrowbody jets routinely using it.) Yet these are for narrow body jets. Once you start looking at wide-body jets, at relatively short fields for these aircraft, I’m sure that there are more issues. These landing weight errors have serious payload (and thus profitability) ramifications for players and are not even remotely close reality, which makes it difficult to forget about when operating to/from these airports with these aircraft in AS.

Yes, of course, this entire conversation is about performance. I was referring to the minutia regarding V1, stopping distances, etc. As far as your example for the B737, I notice that you used the flaps 30 landing chart. Considering that the best flaps settings to use for a short field is 40 degrees, I don’t see how flaps 30 provides a good comparison- especially in the -700 where the threat of a tail strike is diminished. Of course a flaps 30 landing will have a longer distance. Do you have a flaps 40 chart? I would bet that those distances will be less.

To bring the conversation back to the original issue with regards to the AS calculated max payload versus landing distances, I want to bring up one additional point. Through our conversation, it seems to me that AS uses max landing weight as the basis of determining the max landing distance in the game and I do not feel that the MLW should be used to determine payload amount. Let me explain.

With specific regard to how AS calculates usable payload using landing distances, we should be looking at the Max Zero Fuel Weight + about 1 hour of cruise fuel. That 1 hour is based upon a 45 minute reserve plus 15 minutes of contingency, which in the USA is calculated using the fuel flow at the top of descent. I do not know the ICAO standard reserve calculations, but I imagine that they would be fairly similar. For the sake of argument, let’s assume USA regulations. (I know the game only uses one set of “regulations”). I would imagine that AS does not factor in alternates, holding fuel, or anything else extra as those are determined on a case by case basis and would be impossible to replicate in the sim. It just wouldn’t be worth trying either.

The Airbus 320 and the Boeing 737 both have similar fuel flow rates around 5000-6000 lbs per hour or about 2,250 to 2,700 kgs per hour. Lets round that up to 3000 kilos per hour. A quick google search for the A320 finds that the Max Zero Fuel Weight (OEW + Max Payload) is 62,500 kilos (137,800 lbs). If we add 3000 kilos to that, the predicted landing weight that the maximum landing distance (in AS) should be based off of should be 65,500 kgs.

This is far below that maximum landing weight according to the A320 chart you posted a few posts ago. AS should use this number, or something close to it, to determine the maximum usable payload into fields with short runways- not the max landing weight stopping distance. The max landing weight distance should be irrelevant in AS unless it is lower than the MZFW + Landing Fuel number. (Though this is very rare, I imagine that some airplanes it might be an issue). In order for the airplane to land at the maximum landing weight, the aircraft must be carrying a significantly larger amount of gas than the already mentioned 1 hour. This could be for numerous reasons, but none of these are modeled in AS and thus should not be part of the determination AS makes for determining payload restrictions for short field landings.

Again, I suspect that the maximum landing distance numbers (that are used throughout AS) utilize the aircraft specific maximum landing weight distances. As I just mentioned, these are probably all incorrectly removing payload when, in reality, they would not have needed to. This is an incredibly easy mistake to make, and I do not blame AS for making it; but it does cause insidious errors to manifest themselves in short field operations.

I certainly hope that all of this makes sense. I have written and edited this quite a few times, so I may have a typo or some other issue in it. Let me know if you need clarification. It also is getting late- that never helps.

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#11

Boeing doesn’t provide a flaps 40 config chart.

Ah I got It now. Started a discussion within the data team to verify. Should there be a mistake it’s definitely easy to oversee. But I think that there’s really something wrong too.

#12

Thank you for looking into it. If you or the team need any assistance, feel free to reach out to me. I would be more than happy to help. I specifically have access to CRJ200,700, 900 and Embraer 175 charts if that help as well. I fly the CRJ2/7/9 in real life.

#13

Reading this topic just reminds me of another discussion quite a while ago about performances of aircrafts that in real life performed very well on short runways and we can’t put them to use here in AS, on any server.

The biggest example is the operation in some airports in Brazil, such as the SDU airport in my hometown. We operate here the E195/318/319/320/737/738 with a rather ease. The 320 has a limitation to 144 seats and the 738SFP has of 177 seats. In here, if you out any of those planes, except for the 190SR and 738SFP, you can’t operate and those ones you can get only around 30 to 50 seats Max. And there we have another point - the CRJs and ERJs have been known for quite a while for operating in small airports where the vast majority of other planes cannot operate, but you can’t operate de ERJ145 Nor the CRJ200 nor the E190 at the SDU (e.g.) as they should, but the Airbus A220 does it all in almost full payload. So… What’s wrong here?

#14

AS knows about the runway performance problems, but as it would be very time comsuming to implement - rather low on priority. Sorry guys

#15

Thank you for talking with the AS team, but that is disappointing to hear. For a game that touts realism, this is such a glaring issue and the fact that AS won’t spend the time to fix the problem illustrates exactly what is wrong with the game.

Fixing the landing distances should not take that much time. They just need to change the “max landing distance” distances. The rest of their established formulas should stay the same.

#16

I wish it would be that easy. Sadly it isn’t. There’s more than “just” fixing maxLanding. Though you really have a valid point concerning MLW vs. the actual landing weight (OEW+MPL+reserve)

Edit:
regarding the A320-200 in your example. Going the way OEW+MPL+reserves actually ends at a value exceeding MLW according to Airbus sheets. There I’d have read MLW = 64.500 for most weight variants.
65.500 would be close the heaviest variants of the 320ceo which go at 66.000 (corresponding to a MZFW of 62.500). I’d have taken this for a “heavy” variant probably.
Still, generally you have a very good point regarding MLWs

#17

What more is there to do regarding adjusting landing distances?

I know that each airplane’s fuel burn is calculated using distance, not time, and then modified using the absolute value of the difference between the player’s chosen speed and the default aircraft speed. Not 100% accurate, but close enough. Its certainly an easy way to modify fuel burn rates.

Regardless, if you took the kgs/km burned and multiply it by the aircraft default speed, you would get the kgs/hour. That’s the number that could be used for the reserve fuel and it could be a “static” number for each aircraft variant. After that, wouldn’t just taking the MZFW + this calculated reserve fuel value make the “max ‘actual’ landing weight”? After which, you simply look at the landing chart (don’t you have the charts from when you started the game?) to determine the “max landing distance.”

I know that there is a large amount that needs to be changed, but even if you just changed regional jets and the narrow body mainline jets in the short term, and then phase in various other classes of aircraft over time, that would be huge for the players.

As another idea, you could simply make the “max landing distance” equal to 95% of the max takeoff distance. That would make the game’s max landing distance 5% less than the max takeoff distance, allowing for greater and immediate usability in the game. I don’t know all of the backend coding, so I don’t know the varying degrees of coding required in these calculations. I’m simply trying to throw out various alternative ideas that may do something similar in the short term, and would provide additional time for a more thorough and complete revamp of the other performance calculations.

Keep in mind, the 3,000 kg reserve was very much made up. To be more accurate, it would need to be based upon one hour of fuel burn and could be based upon data that you already have regarding fuel burn. (see above) I would do only one hour as it applies the most amount of times and would provide the most amount of operational flexibility.

I do not fly the A320, so I do not have intimate knowledge of it, but after a brief google search, I found this document: A320 Performance

On PDF page 27, or document page 2-1-1, the MZFW and MLWs are located. I have not spent a long time studying the manual, so I don’t know what the various models are referring to; however, I can quickly see that some MZFWs are different, thus allowing for some more “wiggle room” regarding the actual landing weights.

Even if the max landing distances only changed by 5%, that could lead to significant gains in usable payload for these aircraft types because the difference between “minimum landing distance” and the “max landing distance” would change at a higher percentage.

Random example: (not based upon a real aircraft)
Original Min Landing Distance: 2000
Original Max Landing Distance: 2400
Difference: 400

New Min Landing Distance: 2000
New Max Landing Distance: 2300
Difference: 300

Now lets say that the calculated landing weight was at its maximum and the field was 2300 meters long. The payload would have been restricted to 75% using the original numbers, yet would be not restricted at all using the new numbers. In this case, the mere 100 meter change in the max landing distance (4.2% reduction in the max landing distance) had a 25% difference in payload. If the plane could carry 150 passengers, that would be a difference of 37 seats.

I completely recognize that there is a time element in making these changes, yet I feel that there could be a significant benefit made to the game if even a small change was made regarding landing performance.

Sidenote:
As I am writing this, I am wondering if AS calculates the weight of the various individual seats, onboard flight attendants, cargo containers, etc into the individual aircraft’s weight calculation as that would obviously have other ramifications. I don’t feel that these should necessarily effect landing weight from a simplicity standpoint (in the game), but would obviously effect landing in reality.

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#18

Just checked how long it would take. Granted I’d do everything as “exact” as possible, I think it took me an hour to get landing distances for just three aircraft variants. And then I just touched landing distances - which is the much easier part in contrast to take off.
So here’s the values corresponding to your example SLC-SNA:
landing min / max
A320-200 light: 1031 / 1484
A320-200 medium: 1020 / 1493
A320-200 heavy: 1040 / 1514
Differences are barely readable, but the answer is just what was clear already: they are way off in game.
I’ve taken OEW+MPL+1h reserve as suggested by you. AS data.
Actually, would I have simply taken MLW out of the Airbus docs I would have ended up with slightly shorter max. in two of three cases. But it is hard to find a corresponding weight variant for our “light, medium, heavy”.

As you fly the CR9 I’d have a question regarding MLW:
Just like with the A320 data above I found no big difference when looking up data in Bombardier docs regarding MLW vs. MZFW+reserve.
The CL600-2D24 goes at an MLW of 33340 with an MZFW of 32092 except for the first 35 airframes built which had slightly less.
So if I add a one hour reserve of 1288 (value for a 900 NextGen ER in game) to MZFW I’m at 33380.
You tell me how close that 1h fuel is to reality, please, just out of curiosity.

From an engineering point of view I find it quite logically to have MLW certified matching MZFW+reserve fuel.

Still, we both agree that the values are off and would need an update. But IF this ever will be done, it will be a s*load of work to do, particularly if the entire set of data needs to be touched. Boeing, Airbus, Bombardier and Embraer are rather simple as they provide all info necessary. IMHO there are other things that need to be touched first in order to justify such effort I’m afraid.

#19

What document are you referencing those numbers from? I want to compare them to our company manuals to see if the numbers are the same or if the company has modified them. Additionally, I will need to convert your numbers to the imperial system as all of our numbers are in pounds/ feet/ gallons. I’ll look into it and get back to you.

For a quick reference, here is randomly selected flight on the CRJ9. I don’t know if it is the NextGen or not, but they are pretty similar to each other.

This flight is from MSP-CID. Both have plenty of runway and are not limited in any way. There was no notable weather or an alternate. Basically, this is the AS equivalent that we are looking for.

The flight left the gate with a planned 6700 pounds of fuel on board, planned 460 pounds for the taxi out, 2262 pounds (32 minute airborne flight time), had a company standard 750 pounds of gas for an aborted landing, 2460 pounds of reserve (45 min at the top of descent), and a company standard 15 minutes of contingency fuel of 797 pounds. The airplane was supposed to land with 4007 pounds of fuel onboard and then burn 120 pounds of fuel on the taxi in.

Notable Fuel Weights

• Release Fuel (Starting fuel at the gate): 6700 lbs
• Burnoff Fuel (Enroute): 2262 lbs
• Landing Fuel (Reserve + Contingency): 4007 lbs

As far as aircraft weights. This airplane had a Basic Operating Weight (BOW) of 49176 pounds and a planned payload of 13420 pounds (61 passengers). The payload is calculated using the FAA standardized summer weights of 190 pounds per passenger and a planned 1 standard checked bag per passenger (30 pounds/ bag).

FYI, winter weights are 195 pounds per passenger. The difference is solely based upon the calendar date (Nov - April = Winter, May - October = Summer), and regardless of airports or expected temperatures.

In the US, all regional jets are limited to 76 seats and thus that is the configuration of each 900 in our fleet. Our maximum cargo weights in this aircraft are 1700 lbs (in the forward compartment) and 3650 lbs in the aft.

Our CRJ 900s have the following weight limitations:

• Max Ramp Weight: 85000
• Max Takeoff Weight: 84500
• Max Landing Weight: 75100
• Max Zero Fuel Weight: 70750
• Minimum Flight Weight: 45000

I am continuing to research the fuel burn rates, as I am struggling to find a definitive table or chart that shows the various burn rates. We never calculate fuel burn rates as that is a Dispatch function. I will get back to you when I have more.

In practice, your estimated fuel reserve is probably fairly accurate assuming the aircraft is at its max cruising altitude (to lower fuel burn) and considering that it’s a NextGen. In the example I used, the aircraft was filed for only 23,000 feet. (max altitude is 41,000, though typical cruise is at 37,000). After some thought, I would add an additional 10% for taxi in fuel to your “reserve” fuel.

As far as the airframe’s MZFW, it may actually be higher than our company’s listed weight. We only operate using 76 seats in a 2 class configuration. I know the airframe can take many more passengers in a pure economy layout, thus we are in essence payload limited whenever we fly. I “think” the max passenger count is 90 passengers, but I am unsure. Assuming that’s the case, we operate at an approximately 84% max payload.

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#20

First, we never come anywhere close to the MZFW in practice due to max cargo weights.

Assuming that we completely filled every baggage compartment to its maximum weight, all of the bags would weigh 5350 pounds. The MZFW is 70750 pounds.

MZFW - Aircraft Basic Operating Weight - Max Cargo Weight = 16,224
(70750-49176-5350) = 16,224.

If we divide 16224 by 190 pounds, that comes to approximately 85 passengers. Considering that we can only carry 76 passengers, MZFW is unattainable in our aircraft. At a hypothetical 85 passengers, it is of course.

However, this is assuming full cargo compartments. In reality, these aircraft don’t carry that many bags. If we had that much weight onboard, we would have the equivalent of 178 standard bags. 5350/30 = 178. In the US, the FAA states that each standard checked bag (any bag less than 50 pounds) weighs 30 pounds. If the bag is classified as a heavy bag (actual bag weight is greater than 50 pounds), it is considered 60 pounds for weight and balance purposes. If it isn’t a bag (i.e. wheel chairs, powered scooters, etc.), it is weighed and individually added to the bag weights. Even at 85 people, 178 bags is large stretch. Honestly, I’m not sure if 178 bags would even fit on the aircraft. That’s a lot of bags.

For AS, I recommend standardizing the calculation so that each passenger brings with them to only 1-1.5 bag(s). This would scale very easily as the aircraft database already has the maximum allowable seating number and would be a simple arithmetic problem to figure out the maximum expect bag weight. I know that the extra cargo would complicate matters.

For an example, let’s hypothetically say that the manufacturer max passenger amount for the CRJ9 was 85 people. The max expected bag count would be between 85 and 127.5 bags, or between 2550 and 3825 pounds. The passengers would weigh 16,150 pounds. So all told, not counting extra cargo, the max expected payload would be between 18,700 and 19,975 pounds or about 1500-2000 pounds below MZFW depending on the planned bag count per passenger assuming the BOW (49,176) was the same as the aircraft I used above.

To tether this to reality, here is a real-life example:

Real Life CRJ 900 Example:
190 pounds * 76 passengers = 14,440 pounds
30 pounds * 76 checked bags = 2,280 pounds