Cessna 172 front seat weight limit

[GreatLakesFlying]

This is something that has been on my mind since I was preparing for my PPL written knowledge test (not too long ago). The loading graph for the Cessna 172 (attached below) that correlates weight and moment, shows front seat loads for up to 400 lbs. The y-axis itself ends at 450 lbs.

Does that mean that you may not have more than 400 lbs on the front seat? I would think that as long as the total aircraft weight is within limits and the CG is also within specs, there should be no problem for the front seat.

For example, for a Cessna 172P, 500 lbs on the front seat, 40 gallons of fuel, and no other passengers or baggage, the W&B calculations show the aircraft within the normal category of the CG/Moment Envelope (POH p. 6-13) and also within the normal category of the CG limits (POH p. 6-14).

In fact, you can have up to ~ 600 lbs on the front seat and 40 gallons in the tanks, and still remain within the normal category for the CG/Moment Envelope and CG Limits -- based on the 172P POH.

So, why does the pilot and front passenger loading graph end at 400 lbs, in the POH? From an engineering/math point-of-view, the end of the plot means that there is no further information. But as the W&B example above shows, we can fly the 172P with 600 lbs of load on the front seat.

I understand that such load may not be a likely scenario but I am curious about the rationale of ending the plot at 400 lbs and the y-axis at 450 lbs in the POH when the actual maximum -- albeit theoretical -- limit seems to be 600 lbs for the front seats.

 

[Tantalum]

Could have something to do with the physical strength of the seats and max g loads, crash / impact?

 

[James331]

Because humans should only weigh so much.

Back in the days much of the fleet was built, no one imagines humans would grow to be the fleshy land yachts they have become today.

Heck I had a request to transport someone that was 450lbs and 30" wide, that chit isn't even human anymore.

https://healthyeater.com/ideal-body-weight-calculator

Diet and exercise people!

 

[murphey]

Dig out the TCDS for the correct model, it has all the details for weight, position, etc for each seat and each position in the airplane. Don't rely on the chart. The examiner will also be impressed that you know what the TCDS is, and how to use it.

 

[Dan Thomas]

At 450 lb you won't have much elevator travel left. Too much belly. And the legacy Cessna seats were quite light. In '96 FAR 23 required 26g seats in front. They're very strong. Still won't have enough elevator though.

 

[Greg Bockelman]

I don’t think it’s a limit. I think that just happens to be where the line ends. If it isn’t listed in the limits section of the POH or TSDS, just extrapolate the line out and go from there.

 

[Greg Bockelman]

At 450 lb you won't have much elevator travel left. Too much belly. And the legacy Cessna seats were quite light. In '96 FAR 23 required 26g seats in front. They're very strong. Still won't have enough elevator though.

You will have adequate elevator authority if the balance does not exceed the forward limit.

 

[GreatLakesFlying]

At 450 lb you won't have much elevator travel left. Too much belly. And the legacy Cessna seats were quite light. In '96 FAR 23 required 26g seats in front. They're very strong. Still won't have enough elevator though.

A 200 lbs pilot and a 250 lbs passenger on the right seat may have some belly but also have full elevator travel. For sure, a 400+ lbs person in the airplane will be an unlikely scenario. I am curious about the engineering/design rationale for the loading graph to show only 400 lbs for the front seat.

 

[UngaWunga]

At 400+ pounds, maybe they should walk instead of fly. Might do them some good.

 

[James331]

A 200 lbs pilot and a 250 lbs passenger on the right seat may have some belly but also have full elevator travel. For sure, a 400+ lbs person in the airplane will be an unlikely scenario. I am curious about the engineering/design rationale for the loading graph to show only 400 lbs for the front seat.

Designer didn't envision people ever getting that big

 

[GreatLakesFlying]

Dig out the TCDS for the correct model, it has all the details for weight, position, etc for each seat and each position in the airplane. Don't rely on the chart. The examiner will also be impressed that you know what the TCDS is, and how to use it.

In the TCDS for the 172P (or any model for that matter) there are no limitations listed for the front seat load. The TCDS specifies an arm range of +34" to +46" for the front seats, which is also listed in the POH. Even in the aft-most position (+46") you can still load the front seat with 500 lbs and remain within the normal category limits.

I am curious as to why this capacity is not reflected in the POH.

 

[Kansas Flyer]

At 400+ pounds, maybe they should walk instead of fly. Might do them some good.

Have you considered that it's possible to be over 200 lbs and not be Jabba the Hutt?

I'm 6'3" 220 lbs and regularly fly with a friend that is 6'5" 230 lbs. I suppose being tall = fat.

 

[GreatLakesFlying]

Have you considered that it's possible to be over 200 lbs and not be Jabba the Hutt?

I'm 6'3" 220 lbs and regularly fly with a friend that is 6'5" 230 lbs. I suppose being tall = fat.

Some of our friends here seem to have an issue with overweight people. I've ignored their replies because they are not addressing the technical nature of my OP, and are misdirecting the conversation in a manner consistent with trolling. Let us not feed the trolls.

 

[dmspilot]

As written above, the person who created the graph did not envision people weighing over 400 lbs. How high do you expect them to go?

 

[dmspilot]

Have you considered that it's possible to be over 200 lbs and not be Jabba the Hutt?

I'm 6'3" 220 lbs and regularly fly with a friend that is 6'5" 230 lbs. I suppose being tall = fat.

230 is well below 400

 

[Kansas Flyer]

As written above, the person who created the graph did not envision people weighing over 400 lbs. How high do you expect them to go?

The graph is for the combined weight of pilot and front seat passenger.

 

[GreatLakesFlying]

As written above, the person who created the graph did not envision people weighing over 400 lbs. How high do you expect them to go?

The graph represents weight for two persons in the front seat. Are you suggesting that Cessna engineers did not envision people weighing over 200 lbs each, flying side-by-side in an 172?

 

[dmspilot]

The graph is for the combined weight of pilot and front seat passenger.

The graph represents weight for two persons in the front seat. Are you suggesting that Cessna engineers did not envision people weighing over 200 lbs each, flying side-by-side in an 172?

No, you don't have to add them together first before you use the graph.

 

[Kansas Flyer]

No, you don't have to add them together first before you use the graph.

Then why does the graph say "Pilot and front passenger"?

 

[SkyDog58]

Being over 200 lbs myself, this is why I married a 90 lb Chinese girl rather than one of my hometown Indiana corn fed girls.

 

[dmspilot]

Then why does the graph say "Pilot and front passenger"?

Because they have the same arm and are the same line on the graph. They can't put different lines on the graph for each; they're the same line.

 

[Sundancer]

In the C-172's (built in 70's) that I've flown, some with 180 HP conversions, others with 210 HP (T-41), some with extended range tanks, I never encountered a situation where two people in front, and none in the back, got the airplane out of max gross or CG limits. I'm certain we went well over 400 pounds, probably 450 or more, with myself and another bigger guy in front, though probaly never 500 pounds. I mostly stopped doing W&B when it was just me and one other person in the right seat in 172s, though kept at it when I had a pax in the back.

If you're worried about real-world consequences, be more concerned about CG than being at/near/slightly over gross weight. 100 pounds over gross will raise the stall speed about a knot in a 172; if the DA (and runway) are reasonable, a few extra pounds won't kill you; but having the CG too far outside limits will do you in. . .

 

[Clark1961]

Then why does the graph say "Pilot and front passenger"?

It is possible to add them together and use the graph once or keep them separate and use the graph twice and get two moments to be added to the total instead of just one.

 

[FastEddieB]

I can see the same line being used separately for each of two different front seat passengers, each weighing up to 400 lbs.

Though honestly, this has never occurred to me nor come up in real life.

 

[dmspilot]

OK, if I read you right, this is the most reasonable answer so far. You are telling me the idea is to use the graph to find the moment for the pilot, then again for the front passenger, then add the moments to get the total moment for the front seat?

You can do it either way, the math is the same.

The long-range tanks in a Cessna 150 have the same arm as the front seats; the loading line is labeled "Pilot, Passenger and Fuel (Long Range Tanks)". That doesn't mean you are required to add all three of those things before using the graph to find the moment. Most people would probably find it awkward to do so, especially seeing the notation of number of gallons on the line.

Also I will point out that maximum weights for the baggage areas are listed in parenthesis, but not the seats.

 

[GreatLakesFlying]

I can see the same line being used separately for each of two different front seat passengers, each weighing up to 400 lbs.
Though honestly, this has never occurred to me nor come up in real life.

Fair enough (and this goes as a reply to @dmspilot) but the POH does not suggest that we do the front seat moments separately; in fact, the W&B Sample Loading Problem in POH 6-10 (for the 172P, and similarly for other models) shows the front seat occupants' weights added first.

 

[James331]

Edited for kindness

But as someone who works a EMS job that statically a little dangerous, please also think of the people who would be rescuing you when you make those lifestyle choices that result in being very large.

 

[FastEddieB]

Fair enough (and this goes as a reply to @dmspilot) but the POH does not suggest that we do the front seat moments separately; in fact, the W&B Sample Loading Problem in POH 6-10 (for the 172P, and similarly for other models) shows the front seat occupants' weights added first.

Yep! I can see it that way as well.

I think we can agree it’s a bit ambiguous.

 

[Tom-D]

Just a thought, can you be over 200 pounds and have the seat in the full forward position?

In the 170, you load the front seats to max, and with minimum fuel, you will be forward of the forward CG limit.

 

[GreatLakesFlying]

Just a thought, can you be over 200 pounds and have the seat in the full forward position?

From personal experience, yes. I am 220 lbs and 5'10''. When I started training, I was so nervous about having full rudder control that I kept pulling my seat at the full fore position. Admittedly, it made soft-field operations a bit ... uncomfortable in the 172P and 172S I flew, but manageable. Eventually, I grew out of my anxiety and found the sweet spot on the seat railing that allows full rudder control and less belly bruising!

 

[Bell206]

Does that mean that you may not have more than 400 lbs on the front seat?

No. If there is a weight limit it would need to be placarded and entered in the limitations section of the AFM like the baggage compartment weight limits.

So, why does the pilot and front passenger loading graph end at 400 lbs, in the POH?

The charts were formatted per existing guidence. No loading chart will show all possible scenarios. Your limits are most forward and most aft CG calculations. How you stay within those limitations is your responsibilitylity. As mentioned above extending the Y line is one option.

And a quick FYI: if your aircraft has an approved AFM or approved Airworthiness Limitations the aircraft TCDS does not take precedence over those documents.

 

[SkyDog58]

It is possible to add them together and use the graph once or keep them separate and use the graph twice and get two moments to be added to the total instead of just one.

In other words:

Arm(Weight1 + Weight2) = (Arm x Weight1) + (Arm x Weight2)

Math still works.

 

[benyflyguy]

I’d like to see you butter 600 pounds into the front of an 172...

 

[Clark1961]

I’d like to see you butter 600 pounds into the front of an 172...

Are you sure you'd like to see that?

 

[benyflyguy]

Are you sure you'd like to see that?

Lol. The phrase “Baggage may shift in flight” comes to mind

 

[GreatLakesFlying]

I’d like to see you butter 600 pounds into the front of an 172...

Next question?

 

[denverpilot]

In the TCDS for the 172P (or any model for that matter) there are no limitations listed for the front seat load. The TCDS specifies an arm range of +34" to +46" for the front seats, which is also listed in the POH. Even in the aft-most position (+46") you can still load the front seat with 500 lbs and remain within the normal category limits.

I am curious as to why this capacity is not reflected in the POH.

In some aircraft the seats themselves meet a crash-worthiness test at specific G loads. (The Cirrus under parachute comes to mind. The seat is rated to crush or otherwise deform to reduce the G load on the occupant upon vertical arrival at a fairly high rate of speed and save their spine.)

In other aircraft the seat may simply not be rated or tested above a certain weight for anything.

In Cessnas it’d be fairly likely that a supersized pilot or passenger would speed along the standard wearing out of the seat rails which is under an AD and/or cracking it, also in the AD. Most of them aren’t new and have cracking or wear within the limits of the AD and a really large pilot or passenger could be the end of that precarious balancing point, and their ride may trigger thousands in repairs.

From personal experience, yes. I am 220 lbs and 5'10''. When I started training, I was so nervous about having full rudder control that I kept pulling my seat at the full fore position. Admittedly, it made soft-field operations a bit ... uncomfortable in the 172P and 172S I flew, but manageable. Eventually, I grew out of my anxiety and found the sweet spot on the seat railing that allows full rudder control and less belly bruising!

I’m about your stature. 5’ 11” and it’s mostly above my waist. I have to put the right seat far enough forward that my left knee touches the mixture control in the idle cut-off position in my 182 or I can’t get full rudder deflection.

One plus of having done the CFI rating and feeling quite comfortable over in that seat now is that I’m wearing out the right seat tracks now instead of the left ones! Haha. My co-owner can finish wearing down the left ones to the AD limits. I could use the right seat for another ten years probably and not wear that side out. The airplane was flown a lot single-pilot by both previous owners apparently.

 

[JAWS]

From CAR3:

§ 3.390
Seats and berths
—
(a) Passenger
seats and berths.
All seats and berths and
supporting structure shall be designed for a
passenger weight of 170 pounds (190 pounds
with parachute for the acrobatic and utility
categories) and the maximum load factors
corresponding to all specified flight and ground
load conditions including the emergency
conditions of § 3.386.

From FAR 23 (in part):

§ 23.785 Seats, berths, litters, safety belts, and shoulder harnesses.
There must be a seat or berth for each occupant that meets the following:

(a) Each seat/restraint system and the supporting structure must be designed to support occupants weighing at least 215 pounds when subjected to the maximum load factors corresponding to the specified flight and ground load conditions, as defined in the approved operating envelope of the airplane. In addition, these loads must be multiplied by a factor of 1.33 in determining the strength of all fittings and the attachment of -

(1) Each seat to the structure; and

(2) Each safety belt and shoulder harness to the seat or structure.

(b) Each forward-facing or aft-facing seat/restraint system in normal, utility, or acrobatic category airplanes must consist of a seat, a safety belt, and a shoulder harness, with a metal-to-metal latching device, that are designed to provide the occupant protection provisions required in § 23.562. Other seat orientations must provide the same level of occupant protection as a forward-facing or aft-facing seat with a safety belt and a shoulder harness, and must provide the protection provisions of § 23.562.

 

[UngaWunga]

Have you considered that it's possible to be over 200 lbs and not be Jabba the Hutt?

I'm 6'3" 220 lbs and regularly fly with a friend that is 6'5" 230 lbs. I suppose being tall = fat.

Simmer down. He was talking about a single 400lbs passenger.

 

[GreatLakesFlying]

Simmer down. He was talking about a single 400lbs passenger.

Which was never part of this conversation. I started this thread as a technical/engineering one. And, I was careful to frame the questions about the combined load at the front seat, and not make it an issue about a single passenger. I understand that some people have issues with the physical appearance of others, but this thread was meant to be a technical discussion. I cannot control what anyone could write but I appreciate those who were considerate enough to make this an interesting technical conversation about flying and airplanes.