737-900 Weight and Balance Issue

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Old Feb 15, 19, 12:59 pm
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737-900 Weight and Balance Issue

Flight DL985 last night SDQ to JFK

The flight was super empty even empty seats in 1st.

FA Comes on before departure and said "Flights half empty but please do not move from your assigned seat due to weight and balance issues"

Was the FA just trying to stop people from switching seats? or was he serious about the weight and balance?
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Old Feb 15, 19, 1:05 pm
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737-900 are notoriously “tippy” due to the stretched fuselage; there’s even a special tail stand that is often used at the gate to prevent an out of balance condition: https://www.flyertalk.com/forum/27061177-post8.html

The long fuselage and low undercarriage requires care when taking off and landing to avoid a tail strike as well. So, I think a weight and balance warning would be valid in this case.
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Old Feb 15, 19, 1:31 pm
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ahh ok thanks for the link good to know
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Old Feb 15, 19, 3:36 pm
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At least they didn't ask you to lean forward on takeoff!
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Old Feb 15, 19, 3:51 pm
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Also - W&B likely calculated based on current passenger positions (roughly). Thus, if people start shifting around means recalculating, verifying with dispatcher.
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Old Feb 15, 19, 4:20 pm
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Happened to me when I flew UA once into Vegas. Bags beat all of us at baggage claim since they had to unload all the bags before they unloaded passengers.
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Old Feb 15, 19, 7:16 pm
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It's happened to me a few times on regional jets. Usually you are allowed to change seats once you are in the air. Sometimes they will load sand bags in the cargo compartments to help balance the weight.

But we are definitely going to see an accident due to weight and balance sometime soon. The airlines are still using weights from the 1990's. We are a lot fatter now. Everyone should be weighed at check-in.
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Old Feb 15, 19, 7:38 pm
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Originally Posted by FlyinHawaiian View Post
737-900 are notoriously “tippy” due to the stretched fuselage; there’s even a special tail stand that is often used at the gate to prevent an out of balance condition: https://www.flyertalk.com/forum/27061177-post8.html

The long fuselage and low undercarriage requires care when taking off and landing to avoid a tail strike as well. So, I think a weight and balance warning would be valid in this case.
A total piece of garbage aircraft that we, as the flying public, will have to unfortunately endure for at least 20 more years.
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Old Feb 15, 19, 7:48 pm
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Originally Posted by readywhenyouare View Post
But we are definitely going to see an accident due to weight and balance sometime soon. The airlines are still using weights from the 1990's. We are a lot fatter now. Everyone should be weighed at check-in.
It's not a total passenger weight problem on a 739 - it's a center of gravity issue. And the relevant CFR dates from 2005.
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Old Feb 15, 19, 8:19 pm
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Originally Posted by 3Cforme View Post
It's not a total passenger weight problem on a 739 - it's a center of gravity issue. And the relevant CFR dates from 2005.
I realize that. But calculating the CG requires accurate weights. And unfortunately the weights are anything but accurate. In the 1990's a DC-8 cargo plane crashed after takeoff in Miami. Initially investigators thought it was a cargo shift that caused the nose to pitch up and stall. But it was later discovered that too much weight was placed in the rear of the cabin.

The same thing could very well happen on a passenger plane. Only average weights (outdated weights at that) are used in the calculations. All it would take is a bunch of obese people seated toward the front or rear to affect performance. And the airlines will never ask them to move out of fear of not being politically correct.
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Old Feb 16, 19, 4:14 am
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Weight & Balance is determined by zones (zones are groups of seat rows) and for lightly filled flights like you possibly had passengers need to be seated evenly about those zones to ensure that weight distribution doesn't throw the plane's center of gravity too far forward or aft. This can result in the aircraft becoming unbalanced which could turn into a tail strike or an out of trim aircraft enroute.
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Old Feb 16, 19, 3:33 pm
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Originally Posted by readywhenyouare View Post
But we are definitely going to see an accident due to weight and balance sometime soon. The airlines are still using weights from the 1990's. We are a lot fatter now. Everyone should be weighed at check-in.
As someone who worked as a "Load Planner" (AA) in the 90's, I can tell you that the FAA has updated the standard passenger weight charts at least twice since my days. Due to both increasing obesity and more carry on luggage.

Airplanes which are a "stretch" model and/or have aft mounted engines tend to be more "touchy" on the "Center of Gravity" (CG) balance. Smaller planes are more sensitive than larger ones.
For mainline aircraft, very, very few flights would be "border line" enough for concern. But as trained professionals, we know what to look for and would notify Dispatch (who would notify the Flight Crew) if the weight or CG might be critical. Two that always come to my mind when these FT threads pop-up :
  • An MD-80 with less than 40 passengers will need closer scrutiny. Around 20 or less and things will start getting critical. Physical phone calls will be made (vs simple text notes on the load plan). Dispatch is advised to notify the Flight Crew. Confirm that the Gate Agent knows First Class must go out full and all Coach passengers are seated within the 1st "x" rows. Ground Crew Chief is called to confirm 1) everything goes into the forward hold ... no exceptions without calling me. 2) have the sandbag cart ready for ballasting the flight at departure time 3) do not push the flight out until you have confirmed with the Captain that they have called me on the radio to discuss the final load plan. Myself, I will turn off "auto" closeout of the load plan, forcing the pilots to call me before they can takeoff.
  • The 727-200 was a wonderful aircraft in all aspects. Among other things, despite being a stretched, aft engine plane, she was hard to throw out of balance for take-off or landing. However, gate arrival had to be watched ... if the arrival fuel was less than 1800lbs (rare) and if there was more than 5000lbs in the aft cargo hold (rare) then the passengers can not deplane until sandbags (we'd have to calc the amount) were loaded forward.
You seem to know about the "simple version" of the FAA approved passenger weights and how they affect weight-n-balance. As I already implied, most flights are ok with the simple method and have plenty of "spread" from the limits so that there's no concern if the averages are off a bit. When the Gate Agent enters the final passenger count (and count of gate checked bags), all of those passengers are automatically counted as "adults". As the Load Planner, I have a "passenger exceptions" screen where I can adjust some of these "adults" to "kids" (lighter) or "NFL" (heavier). On border line flights, it's fairly common for the Flight Crew to know in advance that I will want a "kid count". I've never asked for an "NFL count" but have had crews call in for an adjustment.

Yes, there are last minute surprises. If a "normal" flight changed to "critical" at departure time, I won't allow the Load Plan to auto close (send the final number to the ACARS printer in the cockpit). The crew will be forced to radio me and we can discuss one-on-one any assumptions/adjustments/stipulations that I've included in the calc.
Failing all of that, the "final numbers" list not only weights and their allowable max values, but also the stabilizer trim (and flap) settings for takeoff. The pilots know their planes and can see if I'm approaching any of the limits, weight or CG. Flaps are a generic setting per aircraft model, but the stab trim is different each takeoff and implies the CG. The crew is free to call me and if the Captain isn't comfortable with an "all adult" (or whatever non standard allocation I used) passenger count, then they can tell me what counts they want me to enter.
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Old Feb 16, 19, 4:32 pm
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Originally Posted by steve64 View Post
As someone who worked as a "Load Planner" (AA) in the 90's, I can tell you that the FAA has updated the standard passenger weight charts at least twice since my days. Due to both increasing obesity and more carry on luggage.

Airplanes which are a "stretch" model and/or have aft mounted engines tend to be more "touchy" on the "Center of Gravity" (CG) balance. Smaller planes are more sensitive than larger ones.
For mainline aircraft, very, very few flights would be "border line" enough for concern. But as trained professionals, we know what to look for and would notify Dispatch (who would notify the Flight Crew) if the weight or CG might be critical. Two that always come to my mind when these FT threads pop-up :
  • An MD-80 with less than 40 passengers will need closer scrutiny. Around 20 or less and things will start getting critical. Physical phone calls will be made (vs simple text notes on the load plan). Dispatch is advised to notify the Flight Crew. Confirm that the Gate Agent knows First Class must go out full and all Coach passengers are seated within the 1st "x" rows. Ground Crew Chief is called to confirm 1) everything goes into the forward hold ... no exceptions without calling me. 2) have the sandbag cart ready for ballasting the flight at departure time 3) do not push the flight out until you have confirmed with the Captain that they have called me on the radio to discuss the final load plan. Myself, I will turn off "auto" closeout of the load plan, forcing the pilots to call me before they can takeoff.
  • The 727-200 was a wonderful aircraft in all aspects. Among other things, despite being a stretched, aft engine plane, she was hard to throw out of balance for take-off or landing. However, gate arrival had to be watched ... if the arrival fuel was less than 1800lbs (rare) and if there was more than 5000lbs in the aft cargo hold (rare) then the passengers can not deplane until sandbags (we'd have to calc the amount) were loaded forward.
You seem to know about the "simple version" of the FAA approved passenger weights and how they affect weight-n-balance. As I already implied, most flights are ok with the simple method and have plenty of "spread" from the limits so that there's no concern if the averages are off a bit. When the Gate Agent enters the final passenger count (and count of gate checked bags), all of those passengers are automatically counted as "adults". As the Load Planner, I have a "passenger exceptions" screen where I can adjust some of these "adults" to "kids" (lighter) or "NFL" (heavier). On border line flights, it's fairly common for the Flight Crew to know in advance that I will want a "kid count". I've never asked for an "NFL count" but have had crews call in for an adjustment.

Yes, there are last minute surprises. If a "normal" flight changed to "critical" at departure time, I won't allow the Load Plan to auto close (send the final number to the ACARS printer in the cockpit). The crew will be forced to radio me and we can discuss one-on-one any assumptions/adjustments/stipulations that I've included in the calc.
Failing all of that, the "final numbers" list not only weights and their allowable max values, but also the stabilizer trim (and flap) settings for takeoff. The pilots know their planes and can see if I'm approaching any of the limits, weight or CG. Flaps are a generic setting per aircraft model, but the stab trim is different each takeoff and implies the CG. The crew is free to call me and if the Captain isn't comfortable with an "all adult" (or whatever non standard allocation I used) passenger count, then they can tell me what counts they want me to enter.
Thanks for the information. One of the NTSB agenrs who worked on the Air Midwest crash had told our class that airlines were using outdated averages and that the NTSB had recommended to the FAA that the use actual weights for a more accurate calculation.

Of course having those actual weights are only useful if people stay in their assigned seats. It really wouldn't do much food on an airline like Southwest.
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Old Feb 16, 19, 10:32 pm
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Does the 753 and 346 suffer the same CG issue?
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Old Feb 17, 19, 12:45 am
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Originally Posted by HWGeeks View Post
Flight DL985 last night SDQ to JFK

The flight was super empty even empty seats in 1st.

FA Comes on before departure and said "Flights half empty but please do not move from your assigned seat due to weight and balance issues"

Was the FA just trying to stop people from switching seats? or was he serious about the weight and balance?
At the end of the day, yes and no ... personally I think the FA was being a bit dramatic, but in all fairness, the FA was likely acting under direction from the flight crew .... and yes, when a flight is less-than-full, there are indeed more concerns regarding weight and balance.

I won't get into CG, % MAC, stabilizer trim, zones, lateral-imbalance, etc, but when nearly empty, there is more room for fluctuation since there are less known weights (I hope that makes sense).

In your case, the weight for baggage/cargo had been established in both the fwd and aft bellies, catering and average pax weight was used to gain a basic W&B for the flt crew to calculate their settings.

As other's have mentioned, some aircraft are notoriously tail-heavy by nature, but again, no need to get into specifics... suffice it to say, yes, there are certain precautions that must be taken, but would there be a noticible impact on CG if a few folks got up and moved?, No, not likely.

The main concern would be if there were a dramatic shift in weight fwd or aft of CG (in this case, let's just say that root of the wing is the CG centerline) ... if pax were not moving from very front to very back or vice versa, there is no major concern.

Don't get me wrong, I've been witness to a B747-400 freighter that could not properly steer due to a miscalculated W/B, the nose-gear was coming off the ground and the A/C couldn't taxi, had to be towed to the gate then fuel added before it could be handled... but on a pax flt, somebody would need to do some real work to cause an issue.
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