Exceeding Max Gross Weight

[JDHelicopterPilot]

Sometimes MGW is a limit of skid gear loading, performance(engine), rotor system design, transmission and much much more. So it is more than metal fatigue and stress on the frame.

 

If you look at the RFM, many helicopters have a provision for increased MGW when doing external load. The reason is simple, the gear can not handle that weight but the rest of the aircraft can. So they allow additional weight only if it is external in which case that load will be applied to the aircraft after the weight is off the skids or wheels.

Edited May 10, 2013 by JDHelicopterPilot

[iChris]

Kinda like the 212...214 and 214B1...same airframe, two have a lot more power...only one is "certified" to use all that power...

 

 

Yes...

 

Different rotor system, trans, and engine...they rest is pretty much the same...

 

That’s ok for the 214B vs. 214B1 but to include the Bell-212 that’s only similar in size and appearance.

 

The B-212 has two engines when combined are still 1,000 SHP less than the single engine (2950 SHP) Bell-214B. The Bell 212 offers a smaller main rotor, smaller tail rotor, about 3-feet shorter in length, 1,500-pound lighter BEW, and 4,000-pounds less external load capacity.

 

However, except for a difference in maximum weight, the Model 214B and 214B1 are identical to each other.

Maximum weight

12,500 lbs. for 214B1

13,800 lbs. for 214B

16,000 lbs. for 214B and 214B1 external cargo operations.

 

Gross weights above 13,800 lbs. must not be imposed on the landing gear.

 

The increase in gross weight is applicable to §29.25[c] or §27.25[c] for part 27 helicopters.

 

With respect to rotorcrafts with jettisonable external loads attached, there is an allowance under §27.25 for an increased maximum gross weight over that established under internal loading as long as the increased weight is jettisonable as an external load. As an example, the applicant would not be required to meet some of the Subpart C and Subpart D requirement of Part 27 at that higher gross weight (i.e. §27.723 Landing gear shock absorption, etc.).

 

Edited May 10, 2013 by iChris

[iChris]

As so often the case, some RFM limitations have nothing to do with the helicopters actual capabilities. Interesting things happen during certification. Without some inside information the, “WHY” is generally lost to myths.

 

The reason for the 2000 fpm rate of climb limitation in the 407 RFM (section 1-9) is quite interesting.

 

There is a requirement to demonstrate longitudinal static stability in the climb at minimum power speed at takeoff power at all weights and centers of gravity. The 407, at light weight, has so much vertical climb performance that the vertical airspeed component would make a very large angle on the pitot tube, making airspeed indications quite unreliable.

 

This made it impossible to do the test in the lightweight conditions required by the FARs. So, the solution was (instead of changing the pitot tube) to restrict the rate of climb. At this limited rate of climb it was possible to make the necessary demonstration of longitudinal static stability.

 

There is no real handling issue, merely a requirement that had to be met.

Edited May 10, 2013 by iChris

[Eric Hunt]

B206 limits are generally 3200 lb with internal load and 3350 with the extra weight on the hook.

 

This is because of a skid limitation, not just for sitting on the ground, but for energy absorption at the end of an auto - so if you cheat by lifting to the hover and then adding an extra person, you might be horribly surprised when the engine quits and the machine crunches through the skids and onto its belly. But if any extra weight is on the hook, it can be pickled and the weight limits are OK for the skids again.

 

The modification to take the machine to 3350 internal is a strengthening of the skids, but you have a Vne of 78kt over 3200lb.

 

The 407 and its 2000fpm ROC limit was also (as I understand it) because of the problem if the engine quits in such a climb - the rotor RPM will decay too much before the machine stops going up and establishes a suitable rate of descent airflow to start pulling the blades around again.

[iChris]

 

The 407 and its 2000fpm ROC limit was also (as I understand it) because of the problem if the engine quits in such a climb - the rotor RPM will decay too much before the machine stops going up and establishes a suitable rate of descent airflow to start pulling the blades around again.

 

It had nothing at all to do with the autorotation capabilities. I don't know where that got started. I've heard it quite a bit. People tying to give reason to a limitation that real wasn’t a limitation.

 

Again, without some inside information the, “WHY” is generally lost to myths. There were a number of articles written and interviews on this issue from people who were present during the certification. Shawn Coyle has even written on this issue.

Edited May 10, 2013 by iChris

[helonorth]

For a long time I, too, thought the 2000' FPM climb limitation was due to autorotation. I read something (I wish I knew where) that quoted Shawn Coyle saying the limitation was due to airflow into the pitot tube above 2000' FPM giving erroneous airspeed indications. He said that rather than trying to redesign the pitot tube, they decided to just put in the climb limitation.

[Eric Hunt]

Well, there you go. Having met Shawn, I would believe what he said.

 

But I wonder what sort of rate of climb would bring the autorotation problem into focus? Anybody got any ideas?

 

Shawn?

[adam32]

 

 

 

That’s ok for the 214B vs. 214B1 but to include the Bell-212 that’s only similar in size and appearance.

 

The B-212 has two engines when combined are still 1,000 SHP less than the single engine (2950 SHP) Bell-214B. The Bell 212 offers a smaller main rotor, smaller tail rotor, about 3-feet shorter in length, 1,500-pound lighter BEW, and 4,000-pounds less external load capacity.

 

However, except for a difference in maximum weight, the Model 214B and 214B1 are identical to each other.

Maximum weight

12,500 lbs. for 214B1

13,800 lbs. for 214B

16,000 lbs. for 214B and 214B1 external cargo operations.

 

Gross weights above 13,800 lbs. must not be imposed on the landing gear.

 

The increase in gross weight is applicable to §29.25[c] or §27.25[c] for part 27 helicopters.

 

 

And all BASED on the same airframe, so that airframe can handle what the 214 throws at it, so if you overload a 212 the airframe should handle it. That's what I was getting at, the structural integrity part of this thread that was brought up earlier.

 

And yes, the 214 and 214B1 are the same exact aircraft, so why does one have a higher gross then the other?

[JDHelicopterPilot]

It had nothing at all to do with the autorotation capabilities. I don't know where that got started. I've heard it quite a bit. People tying to give reason to a limitation that real wasn’t a limitation.

 

Again, without some inside information the, “WHY” is generally lost to myths. There were a number of articles written and interviews on this issue from people who were present during the certification. Shawn Coyle has even written on this issue.

I heard similar information from a factory instructor. He stated he knew of an accident in which the aircraft was climbing at a high vertical rate which an engine failure. The pilot was unable to get the collective down fast enough and recover rpm to fully enter an auto prior to impact.

 

I can see where loosing an engine with excessive AOA could result in rapid loss of RPM where in some cases RPM may not be fully restored in time.

[helonorth]

Since Shawn Coyle did the certification testing on the 407, he should know. Look at the last post on the page. A lot of 407 pilots and instructors are still repeating the autorotation thing.

 

http://www.pprune.org/archive/index.php/t-56729.html

Edited May 10, 2013 by helonorth

[Rupert]

Back in the 70's you had to bust the FAR's or you wouldn't have a job. I thought that had changed.

 

If anything goes wrong, your employer will deny everything and throw you under the bus. Guaranteed. Without an apology or a second thought about it.

 

Out of CG (especially forward) and over gross will bite you in the butt if you have to do an auto. Gasoline and pistons...bad. Sudden silence. Happens too often.

 

Sorry to hear that things haven't changed with small operators. The big boys know better. One accident undoes whatever profit you made from violating the FAR's.

 

As the chief flight instructor what you should do.

[JDHelicopterPilot]

Since Shawn Coyle did the certification testing on the 407, he should know. Look at the last post on the page. A lot of 407 pilots and instructors are still repeating the autorotation thing.

 

http://www.pprune.org/archive/index.php/t-56729.html

I understand fully. Just stating what was told to me from an B407 instructor. Take for what it is worth. I do agree with Shawn on the actual reasons for the limitation.

 

However, I do think there is some merit in discussing the effects a high AOA will have on RPM decay and the ability of a pilot to then recover that RPM following a surprise engine failure at low altitude.

[iChris]

I understand fully. Just stating what was told to me from an B407 instructor. Take for what it is worth. I do agree with Shawn on the actual reasons for the limitation.

 

However, I do think there is some merit in discussing the effects a high AOA will have on RPM decay and the ability of a pilot to then recover that RPM following a surprise engine failure at low altitude.

 

Nick Lappos also wrote about these issues:

 

 

The climb is an especially difficult case because the power input to the rotor is high, and the trimmed collective position is high, so the initial rotor decay is very fast. This makes the minimum rotor droop lower than in a level flight case, if everything else was equal. Combined is the fact that the climb inflow is farther away from autorotative flow means that there will be much more delay before the autorotative flow can drive the rotor.

 

Offsetting these negative effects is the fact that the tests performed for certification include auto entry in virtually all-critical flight conditions, including climb. The FAA inserts a delay to simulate the reaction of an average pilot, and the climb is a maneuver state where the hand is actively trimming the power, so the delay in pilot reaction in a climb is very much less than a leisurely cruise. The FAA allows 1.3 seconds in cruise before down collective, but only .3 second for maneuver states such as the climb. This means that the auto entry is permitted to occur more quickly in tests (as it would be in reality). The net result is that auto entry from the climb should be not much worse than cruise.

 

 

 

The answers are common to all helos, not just the Robinson, frankly.

 

The climb limitation for most helos is generally due to the somewhat silly handling requirements of FAR, where the longitudinal stick stability is measured at max climb rate. Some helos have difficulties meeting it, so they impose a climb rate limit at the highest climb rate where the handling is still compliant.

 

We have Bell lurkers on PPRuNe, wonder what they would tell us?

 

bladewashout asks a good question. Do we fly as if the engine will quit right now, and fly in every way to completely optimize the response to that failure? Best engine failure protection, for those who would completely slave their flight techniques to minimize the risk of engine failure: Stay Home.

 

It is a probabilities game we play when we fly, order a steak or pull down our pants. Because we train for engine failure, it becomes THE failure, and we focus on it as if it were the ONLY failure.

 

 

REF: Engine failure in the climb question

Edited May 11, 2013 by iChris

[JDHelicopterPilot]

I still wonder, even with the delay the FAA includes if this is enough. I have seen many accidents where the autorotation did not end well. It is one thing to be out testing the aircraft for auto rotations and another to have a surprise engine failure. A recent HEMS accident in an AS350 shows us just how important a proper entry into an auto is following an engine failure. This particular pilot failed to enter correctly and did not have enough time to recover lost RPM. The result was fatal.

[aeroscout]

In the OP's original scenario he talked about being 50 lbs overweight. That's about 7 to 8 gallons of fuel, if my calculations aren't too far off. One reply said to turn it and burn it (to paraphrase). some fuel trucks have built in defuel capability iow the ability to suck gas out of a tank. You could take an extra large fuel sample. Or you could siphon it out yourself.

One reply talked about metal fatigue with perfect memory, another replied that wasn't necessarily true, and I agree. For airframe and power train and lifting surfaces there is a built in load and gust factor.

Another reply talked about landing gear limits. This is especially true with oleo components in the landing gear.

The other pilot was mentioned, and I agree with the thought that the negligent or ignorant or reckless pilot gives the conscientious pilots severe handicap to overcome. This particular problem is exacerbated in multi engine aircraft. When a pilot tells his boss their multi engine aircraft cannot take off full fuel, full seating capacity, and full baggage there have been occasions when the conversation is interrupted by a pilot in the exact model of aircraft doing the very thing you just told your boss you couldn't do.

Pilots are very often their own worst enemy.

 

 

edit revision

Don't be your own worst enemy.

Edited May 12, 2013 by aeroscout

[ridethisbike]

 

The other pilot was mentioned, and I agree with the thought that the negligent or ignorant or reckless pilot gives the conscientious pilots severe handicap to overcome. This particular problem is exacerbated in multi engine aircraft. When a pilot tells his boss their multi engine aircraft cannot take off full fuel, full seating capacity, and full baggage there have been occasions when the conversation is interrupted by a pilot in the exact model of aircraft doing the very thing you just told your boss you couldn't do.

 

 

That, to me, is the other pilot attempting to throw me under the bus. He wasn't a part of that conversation and he should have stayed that way. I would stare that pilot dead in the eye and reply "Well here are the numbers that say, legally, you can't."

 

If I'm getting thrown under the bus like that, you better hold on tight because you're coming with me and it's going to be a bumpy ride...

[aeroscout]

 

That, to me, is the other pilot attempting to throw me under the bus. He wasn't a part of that conversation and he should have stayed that way. I would stare that pilot dead in the eye and reply "Well here are the numbers that say, legally, you can't."

 

If I'm getting thrown under the bus like that, you better hold on tight because you're coming with me and it's going to be a bumpy ride...

I see what you mean, and I agree that you are most certainly right.

I on the other hand may not have made my full meaning clear. By interrupting the conversation I meant that "the boss" in my example sees the same exact make and model aircraft roar down the runway (after my boss watched him load and taxi) in the middle of me telling him I can't do what that pilot is in the process of doing, and thereby making the process of him going under the bus with me much more difficult.

I apologize for not explaining my meaning better.

[Mikemv]

Guys,

 

If you told your boss that as PIC you know your responsibility is to "Protect the Sacred Trust" that passengers place in you to complete the flight without harm or fatalities.

 

I would point out that the other aircraft is risking the lives of all on board and ask the Boss would he like you to risk the lives of his family and passengers?

 

Telling him that your primary concern is always the safety of flight and you will never risk anyones life for fuel, baggage or another pax.

 

Being in this situation for 26 years, my former employer would say "He does not always say what I want to hear but we will never be endangered by my requests being met".

 

Mike

[Nearly Retired]

Well Mike, I guess it comes down to how much risk a boss is willing to accept. People In Power are generally risk-takers. They didn't get to where they are by being ultra-conservative or wishy-washy. They know that sometimes achieving something involves a certain level of risk over and above what "normal people" are willing to undertake.

 

My old boss was like that - in and out of the helicopter. We used to operate in and out of some truly horrible LZ's. Some of them were such tight hover-holes that I'd limit it to just him and me and just enough fuel to get home or to a gas station - well below our regular 3200 pound MGW. Even so, I was hanging it out for a time on every landing and every departure. It was risky. I knew it; he knew it. But was it "dangerous?" That's the judgment call.

 

On the other hand, weight and balance numbers are black and white limitations. But bosses who have been around aviation for a time (as mine had) know that the aircraft won't fall out of the sky if those numbers are exceeded. They know, for instance, that even in a 206B if you take off 50 pounds over gross (if you have the running room), fuel burn will get rid of that 50 pounds pretty quickly. (Twenty-six gallons per hour is 176 pounds per hour or three pounds per minute. So that 50 pounds will be gone in about 15 minutes or so.)

 

My former boss then bought a jet (which I did not fly). You think there's some hanky-panky going on in the helicopter world? Feh- you should see the fixed-wing side. The runway at the airport they're based at is *just barely* long enough for the jet...*IF* they keep the weight down, which usually means limiting the number of pax *AND* an immediate stop for fuel at an airport with longer runways. Does the boss do that? Oh no! I've seen him go blasting off with a full load of people and enough fuel to get where they're going. The airport manager tells me they do it all the time even when I'm not around to witness (and especially since I've left the company). The boss knows that what they're doing is not by the book and involves a certain amount of risk. The crew knows too, but they do it anyway because they are hotshot jet pilots. It's all fine as long as everything goes perfectly. But one day they'll blow a tire or something and you'll read about them in the paper.

 

So you can't say that bosses will always honor and respect the lines in the sand that you draw. If you're one of these types of people who puffs his chest out and says, "I'LL NEVER VIOLATE ANY RULE, REGULATION OR LIMITATION...EVER!" you will find general aviation to be a difficult, uncomfortable industry. Because one day you'll be driving with other people in the car and you'll be doing 55 in a 45 and some smart*ss in the back seat will snidely comment, "So...you never violate any rules, eh, Mister By-The-Book?"

 

Well of course we do. We all do. We do it all the time when *WE* think it's appropriate. You might proclaim to the world, "Well I might violate other insignificant or trivial rules or laws when necessary or convenient, but I will *NEVER* fly even one pound over-gross!!"

 

Yeah. Good luck with that attitude.

 

I'd be out in the Gulf of Mexico with my LongRanger, just before dawn on a Thursday, ready to do the crew-change of platform workers. They'd give me a manifest of people and bags showing 1050 pounds. I'd then fuel to MGW for the trip to "the beach" (a 17 minute flight). And as I'd fuel the helicopter to precisely 170 pounds, I'd wonder just how accurate the fuel gauge is in the midrange? Then I'd wonder if everyone actually weighed theirselves and their baggage, considering the platform we lived on had no scale for such a thing.

 

I finally came to the conclusion that it was virtually impossible to guarantee a certain takeoff weight with any accuracy. I'd put my 170 pounds of gas in, hoping that I'd be "close enough" on the GW, but knowing and accepting the fact that I might be as much as 10% off in either direction.

 

Ten percent of 1050 pounds is 105 pounds. Ten percent of 170 pounds of fuel is 17 pounds. Total that we "might be" off? 122 pounds on 4150 pound helicopter.

 

How anal do you want to be?

[Mikemv]

NR,

 

You are going to fly as you wish.

 

I told you about my mentality of flying safely.

 

There was no puffing out my chest or drawing lines in the sand. There were values that were upheld, just that simple. Just my mentality about flying.

 

As a member of the IHST Safety Committee and mentor of many pilots, I say what I do about not intentionally and knowingly exceeding limits. I will not tell anyone it is OK to exceed a limit.

 

Everyone will do as they wish no matter what any of say on an internet forum.

 

Best Wishes,

 

Mike

[Nearly Retired]

Mikey, I apologize, I guess I should have made it clear that I was not speaking directly to *you* when I made that comment about pilots who puff their chest out and proclaim this or that. I was speaking generally. For I have known such pilots who make these ridiculous statements about never violating aviation rules or laws, and then they go out and do it anyway in some manner in their "real life." It's the inconsistency that bothers me.

 

I'm just saying that we should never, ever, ever speak in absolutes. Not ever.

[SBuzzkill]

On the military side of things we try to be as accurate as we can be on weight and balance. We weigh ourselves with our gear, review the w&b forms and add in armament and gas, etc. In my airframe we are always loading to max gross weight if we are taking ammo. Which side of the line are we on? How many guys weigh themselves with a CSEL, an M4, NVGs, and magazines? You can be conservative and overestimate your weight, but then you could be cheating yourself out of an extra rocket or 10 minutes of fuel. How accurate is the fuel gauge? Will the FARP guys stop exactly when you tell them to? How much dirt has been brought into the helicopter since it was weighed?

 

When you're always that close to the line you're never going to know for sure whether you are over or under. You just have to try your best with the time and the tools you have.

Edited May 12, 2013 by SBuzzkill

[JDHelicopterPilot]

We weigh all crew and pilot in flight gear. All equipment brought along is pre weighed. Weight of the aircraft and fuel is a know number as well. We are then allowed to use estimated passenger weight plus 10lbs. If the passenger is really large we may ask the hospital to do an actual weight and measurement. For scene calls it is estimated plus 10lbs always.

 

Since it is a twin engine helicopter I am required to determine CG. In our A109s we were able to develop a loading schedule by showing weigh configurations to the FAA and that in those configurations there was no way to exceed CG limit. With that approved I don't need to do an actual CG calculation.

 

In our EC135 we have to do a manual calculation but have been approved to use a PDA and I am sure later will be approved for iPads.

 

So, there are ways to be able to avoid plotting out or calculating CG for each flight if you can show that in said configurations it is impossible to exceed it. The FAA will sign off on it.

[ridethisbike]

 

I'd be out in the Gulf of Mexico with my LongRanger, just before dawn on a Thursday, ready to do the crew-change of platform workers. They'd give me a manifest of people and bags showing 1050 pounds. I'd then fuel to MGW for the trip to "the beach" (a 17 minute flight). And as I'd fuel the helicopter to precisely 170 pounds, I'd wonder just how accurate the fuel gauge is in the midrange? Then I'd wonder if everyone actually weighed theirselves and their baggage, considering the platform we lived on had no scale for such a thing.

 

I finally came to the conclusion that it was virtually impossible to guarantee a certain takeoff weight with any accuracy. I'd put my 170 pounds of gas in, hoping that I'd be "close enough" on the GW, but knowing and accepting the fact that I might be as much as 10% off in either direction.

 

 

 

Yea, but as stated before, there's a difference between intentionally and knowingly flying over max and unintentionally doing it. In the case you just made, with the numbers you were given, you did what you could about keeping it under max. If you were over max, the only way you would know is if you weighed everything out yourself and wasted MASSIVE amounts of time. You get handed numbers by people whose job it is to do these things and work with it.

 

Now had you topped the tanks knowing you'd be over max... kinda dumb.

[aeroscout]

Guys,

 

If you told your boss that as PIC you know your responsibility is to "Protect the Sacred Trust" that passengers place in you to complete the flight without harm or fatalities.

 

I would point out that the other aircraft is risking the lives of all on board and ask the Boss would he like you to risk the lives of his family and passengers?

 

Telling him that your primary concern is always the safety of flight and you will never risk anyones life for fuel, baggage or another pax.

 

Being in this situation for 26 years, my former employer would say "He does not always say what I want to hear but we will never be endangered by my requests being met".

 

Mike

While I like your post and agree with it, I do take issue with one aspect. Maybe it's semantics, or even polemics, but in aviation safety is never my primary concern. My primary concern is accomplishing the assigned flying task, if possible. Safety should be a natural by product of operations. In that sense no unwarranted risks should be taken as to jeopardize the accomplishment of the assigned flying task. I used to tell my boss that I like to get him and or his passengers there in one piece. I apologize in advance if that sounds argumentative.

 

PS In an earlier post of mine in this thread I talked about oleo struts. Many manufacturers also list a max taxi weight as a limitation on the landing gear, the associated attachment points and the rest of the airframe, That weight will exceed max takeoff weight by a slight amount. That amount is on the order of less than one percent and is intended to allow fuel burn off for startup taxi and takeoff. If you haven't burned off said fuel you must delay your takeoff until you do. Also, as has been stated before, atmospheric conditions can certainly further restrict max takeoff gross weight whereas I am not aware that any atmospherics will reduce max taxi weights.

Edited May 12, 2013 by aeroscout