Turbulence and feet per second

[ImaginedByGod]

The area that I have been flying is bumpier than what I'm used to, and I want to calculate or find a cruise speed that will not 'break' the plane if turbulence is encountered, but also maintain a reasonable airspeed.

I've been doing lots of research, and it seems like people are pointing to using Maneuvering speed. The problem is that Maneuvering speed in my plane is rather slow....about 110-120 kias. The aircraft that I'm using at the moment is the Cessna 210. For the most part, I find that people cruise around 145 kias, but can go up to 155 or even Vno. They tend to maintain that speed through light-moderate turbulence and not bother adjusting the power. My concern is the potential of increasing the load factor on the wings and thus over stressing the plane.

This has lead me to become curious lately about V speeds, specifically Va (maneuvering speed), Vb/Vra (rough air penetration speed), and Vno (maximum structural cruising speed). I have been looking, with no joy, for a formula to calculate Vra.

From what I've been reading, in GA airplanes, Vno or the top of the green arc is a speed at which the aircraft is able to withstand up or downdrafts of up to 30 feet / second without over loading the plane. The question then arrises, What category of turbulence is 30 FPS? Light? Moderate? In any case, if severe turbulence, or even sustained moderate turbulence is encountered, slowing to or below Va is probably a good idea.

To sum it all up, what I'm looking for is a way to find or calculate Vra, and understanding turbulence in terms of feet per second.

Thanks ;)

[The Bunglerat]

Admittedly, it's been quite a few years since I flew lighties, & furthermore I never had the pleasure of flying the C210. That said, most aircraft flight manuals publish a turbulence penetration speed, & failing that: a manoeuvring speed.

My point being: If the manufacturer publishes a recommended speed, then that's the speed they recommend, so that's the speed you fly. Simple. And with that being said, why bother trying to reinvent the wheel if the manufacturer has already done the math for you? Of course, it will mean having to slow down - which can be frustrating, I know - but them's the breaks. And 'break' you just may if continually ignored, especially with the age & fatigue issues facing so much of the GA fleet these days.

[sagan]

From what I have found.

Light - 5 Feet Per Second - 20fps
Mod - 20fps - 35fps
Severe - 35fps - 50fps
Extreem- >50fps

Maneuvering speed Va is the speed at which the wing will stall at the limit load of 3.8g
( remembering 1.0g of that is in level flight)

The wing will be over stressed at 3.8g above Va and potentially fail at 5.7g ( 150% above the limit load )

That's positive load factors, I think most aircraft are stressed for less in negative g ? At least the Vn diagram I was looking at has that.

[alphacentauri]

Sagan is right.

From the Manual of Aviation Meterology, chapter on Turbulence

Light = 300-1199 fpm
Moderate = 1200-2099 fpm
Severe = 2100-2999 fpm
Extreme = >3000fpm

If you divide the above numbers by 60 you will get the numbers quoted by Sagan. Just highlighting where the numbers come from.

My rule of thumb when flying survey operations. Avoid Extreme turbulence at all costs. Avoid severe turbulence where possible and, if encountered or flying in forcast area, fly at Va.

Fly at Va if your in moderate turbulence.

Proceed with caution in light turbulence.

Its also worth noting that Va can change with aircraft weight. For the aircrat I flew Va was painfully low when you where light. The heavier the aircraft the better. We used to calculate it for take off and landing weights for each flight. This info should be in the AFM

Alpha

[rioncentu]

Yes Imagined I too have asked the same question and never got an exact answer.

On descent in the 210 you easily approach the top of the green arc and must be vigilant to keep from exceeding that.

My Manouvre speed is 125 knots which is a hell of an excercise to reduce to on descent if things get rough.

I will watch this thread with interest.

[T28D]

The C210 is deliberately limited by Cessna to avoid overstress in the un strutted wing/fuzelage attach area.

This has been the subject of debate for years but the end conclusion is that the way the wing attaches does warrant care in turbulent conditions.

[Oktas8]

Good question, and one I've wondered about too. I have no written references, so what I say is open to correction. However...

My understanding is that Va is a little too slow for best performance in turbulence. Yes, it protects the aircraft from structural damage due to excessive g load. But you could inadvertently stall in severe turbulence, which is just as bad.

Rough air penetration speed, or turbulence penetration speed, is around 5% to 10% faster than Va to reduce the risk of stalling. I don't know the precise calculation. The manufacturer expects the pilot to maintain an attitude in turbulence, specifically not to try to maintain an altitude, and this will reduce the chance of structural overload.

Here's what the good people at FAA.gov require (gusts are assumed to be 50fps according to rule 23.333, and the speed Vc is equal to 33 times the MTOW (lbs) divided by wing area (sq feet) according to rule 23.335.)
(d) Design speed for maximum gust intensity, VB. For VB, the following apply:
(1) VB may not be less than the speed determined by the intersection of the line representing the maximum positive lift, CNMAX, and the line representing the rough air gust velocity on the gust V-n diagram, or VS1√ ng, whichever is less, where:

(i) ng is the positive airplane gust load factor due to gust, at speed VC, and at the particular weight under consideration; and

(ii) VS1 is the stalling speed with the flaps retracted at the particular weight under consideration.

Couple of extra things, from others' posts above:

- Va protects against a single full and abrupt control input. It does not protect against multiple controls used simultaneously, or against one control input made multiple times.
- If using aileron and elevator together, the rule of thumb is that the actual 'g' limit is only two thirds of the basic limit. This is called the rolling g limit. Note also that for aerobatic aircraft, the entry speed for a flick roll is very much lower than Va.
- Va does not protect against multiple sequential inputs of the same control surface. If for example, at Va, you apply full left rudder then immediately full right rudder, you can expect to break something.
- Va does not necessarily protect against full forward stick. If you want to mess about with high negative 'g', Va is not the number to use.
- Va is not necessarily about the wing. The wing spar is usually over-engineered. Va might be limited by the tailplane or fin strength, or even by the strength of the aft fuselage (which takes a huge bending load at high g.) It is possible that the first item to fail might even be the engine mounts, or other high-load points inside the fuselage.

(Edit - I don't know much about the C210. My comments in the last sentence are for light aircraft generally, not the 210.)

Cheers,
O8

[rutan around]

IBG I've just retired after completing 18 years and 4000+ hours flogging a C210 around the northern parts of Australia. I too used to worry about what was acceptable turbulence until I attended a Systems and Procedures course for C210's put on by the Cessna Pilots Association. The instructors were very knowledgeable and one had worked for Cessna as a test pilot during the testing of some of these aircraft. Someone asked him when was turbulence bad enough to require cruise speed reduction. He said when you're hitting your head on the roof every 30 seconds or so. He said they are very strong and we shouldn't worry about moderate turbulence.

I tend to adjust my speed to the level of comfort I need. I'm too old to be bounced around in a hot uncomfortable cockpit in order to save 5 minutes. If it's hot and you just know it's going to be rough below 8000 stay up in the cool smooth air until the time to destination in minutes equals the number of thousand feet you have to lose. Then drop the U/C. A C210 will come down nicely @ 1000 fpm and you will see a stable 140-145 K indicated without any of those scarey 160K excursions sometimes seen descending in turbulence with U/C up.

We were told that wing failure in strutless 210's invariably occurred beyond VNE. The wing fails at the point where the flaps end and the ailerons start. The outboard section bends and breaks downwards because at very high speeds this outboard section is at a negative angle of attack due to the large washout in C210 wings. All it takes is a big aileron input (such as our hero pilot would do as he came out the bottom of a cloud and found himself looking at the ground sideways) to provide enough additional downward force to fail it.

One other worry I used to have. In dry season if you take your headset off in flight you often hear dreadful noises which sound like the carry through spar is on it's last legs. It is actually the windshield which is fitted loose so it doesn't crack. When it moves about only a minute amount it makes these noises that you would never want to hear from your spar.

So to sum up: to fly smooth, safe and worry free fly high, descend slow, don't exceed VNE and don't take your head sets off.

Cheers, RA

[Tarq57]

I think I'd rather inadvertently stall in turbulence than have something break.

That said, whenever I've flown in fairly bad turbulence, on the "airspeed dropping rapidly" side of the 'bump' there seems to be a corresponding large decrease in loading. Down to zero G, maybe a bit negative. Stall speed at zero g is zero. (control will be a tad difficult at this speed, though.;))

I think it would be difficult to stall in turbulence, and the only severe encounters I've had, I've reduced to below Va, because the airspeed excursions easily shot the airspeed to well above Va, albeit briefly.At the other end of the green range, in the same turbulence, the stall warning operated, once again, briefly, and this also corresponded with much reduced loading.

[Wally Mk2]

Good post there 'rutan':-) 4000 hrs in a C210...you poor bugger!:E

Much has been written about turbulence & is a very subjective subject.
What one pilot would do to reduce it's effects on airframes & pax could be somewhat different to the next pilots reactions or lack thereof.
Often yr cruising in light turb at a typical cruise speed then hit almost severe trub in an instance & that being the case the recommended turb penetration speed for such a situation is instantly exceeded so like most things in aviation ones personal comfort factor is yr guide here.The book No's are really only a guide in some ways.



Wmk2

[MakeItHappenCaptain]

Light;

Occupants may feel a slight strain against seat belts or shoulder straps. Unsecured objects may be displaced slightly. Food service may
be conducted and little or no difficulty is encountered in walking.

Occasional – Less than 1/3 of the time.

Intermittent – 1/3 to 2/3.

Continuous – More than 2/3.


Moderate;

Turbulence that is similar to Light Turbulence but of greater intensity. Changes in altitude and/or attitude occur but the aircraft remains in positive control at all times. It usually causes variations in indicated airspeed.
or
Turbulence that is similar to Light Chop but of greater intensity. It causes rapid bumps or jolts without appreciable changes in aircraft altitude or attitude.

Occupants feel definite strains against seat belts or shoulder straps. Unsecured objects are dislodged. Food service and walking are difficult.


Severe;

Turbulence that causes large, abrupt changes in altitude and/or attitude. It usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control.

Occupants are forced violently against seat belts or shoulder straps.
Unsecured objects are tossed about. Food Service and walking are impossible.


Extreme;

Turbulence in which the aircraft is violently tossed about and is practically impossible to control. It may cause structural damage.


The Vb speed (turb pen.) is not usually any different from the Va speed for light a/c and is defined at 66'/sec of vertical gust.

In general, any time you are in moderate turbulence you should be not above the Va speed adjusted for weight.

Note, even though it is expressed that you will not break the aircraft if you make full deflection at Va, DO NOT go from one full deflection (eg. Full left rudder) to the other extreme.:=

[ImaginedByGod]

There's some great information on this. Thanks everyone!

[rutan around]

IBG
Wally is quite right-turbulence is a very subjective subject. Based on Makeithappencaptain's excellent definitions I slow down in moderate chop and the less moderate it is the more I slow. "Loose objects moving about " would be an easy way to judge that it's time to slow down. Perhaps you could place your mob phone on the glareshield and rename it your "Oh F*#k-o-meter" When the meter goes up you slow down.
Safe Flying RA
As the young pilots apple cheeked old grandmother used to say " I want you to be real safe so you fly real low and real slow"

[Lasiorhinus]

MIHC, Ive always found it difficult to walk around in a 210, regardless of how strong the turbulence is...

[Lancair70]

Totally agree Lasiorhinus. LMAO

The above guide, whilst it is well written for an airliner, does it really apply to a lighter a/c ?

Ive been flying and encountered what I feel as top end of moderate turbulence in the circuit area in a C182. Later visually seen other light a/c getting bumped around in the circuit, but watching a 737 on downwind it appeared to be smooth as silk ?

Is it the same as comparing a 4.5m aluminium boat to an 80m floating gin palace ?
I can tell you the ride difference between a 4m tinny to an 8m fibreglass boat in 2 foot chop is spine breaking to champagne sipping.
Are these comparisons fair ? Both are basically vehicles travelling in a fluid environment although water is somewhat harder.

[thorn bird]

There's the old coffee test for turbulence.

If the coffee is just slopping about within the cup its light.

If its slopping out of the cup its moderate.

If you cant find the cup its severe.

[Ex FSO GRIFFO]

Onya Mr RA for an excellent explanation.

I did not know about the windshield being fitted 'loose' in the 210.
However it does tell me why, in VH-KWW for example, the windscreen used to creak like crazy - especially on the descent, so I used to slow it down using the u/c method to keep it 'within my tolerances'.

But, alas, it was still full of 'internal' cracks which were a 'bugger' in the afternoon sun when landing to the west...

One 'famous' 210 driver in WA wrote this one up -
'Windscreen creaks badly on descent - frightens passengers - F#*in' TERRIFIES pilot!'

Cheers:ok:

[MakeItHappenCaptain]

Las and Lanc,

Yeah, but these are the quoted "definitions" so I'm not complaining when the skimpy passes me a coffee from the middle row.:E

"Eh pahlut, you wanna drink? It's inna VB can but":}

Actually, maybe this is a complaint in a way.......

[ImaginedByGod]

Now all of this food for thought has brought me to another question.....

How many G's can Light, Moderate, and Severe turbulence produce based upon their prescribed FPMs? I'll do some more digging and see if I can find a rate for 'Gravities'.

[MakeItHappenCaptain]

Your question's answer is relative to the airspeed of the aircraft. The faster you travel for a given vertical gust, the smaller the resultant change in relative airflow.
WRT the lift formula, a 10% increase in speed will give an 11% increase in lift and (as LF=L/W) the resulting LF. Then you need to factor in the changing Cl as AoA varies, so you really need to look at it on a type by type basis if you want an accurate answer.

All you need to know is that going faster than Va in moderate or higher turbulence is bad.:cool:

(Another way to think of it is that it won't matter how deep it is, you'll be in the siht regardless.)

[Oktas8]

If the coffee is just slopping about within the cup it's light. If it's slopping out of the cup it's moderate. If you cant find the cup it's severe.

That one goes on my "quotes to memorise" list. Thanks TB!

Just an extra thought. If you do go too fast in turbulence, don't expect anything to "break". What will happen is reduced airframe life and possibly some very slight bent parts, by no means necessarily the wing itself. Airframe abuse is often insidious and hard to detect.

But I continue to use turbulence penetration speed to penetrate moderate turbulence, assuming of course I haven't been able to avoid it. If it's not quoted, I guess Va is a close approximation, even if you're one of the nine out of ten pilots* who don't factor it for aircraft weight at the time.

* Personal experience from examining. Present company excluded, naturally!

[das Uber Soldat]

Just an extra thought. If you do go too fast in turbulence, don't expect anything to "break". What will happen is reduced airframe life and possibly some very slight bent parts, by no means necessarily the wing itself.

You seriously test people?

http://www.brisbanetimes.com.au/ffximage/plane_wideweb__470x307,2.jpg

[MakeItHappenCaptain]

Gotta agree with Uber on this one.

The difference between the limit (normal ~3.8) and the ultimate LF (+50%) might apply when the aircraft is new, but metal has memory and every time it gets flexed back and forth (ie by exceeding Va in bumpy stuff aka overstressing the airframe), it weakens just a bit further.

How long until the ultimate LF is equal to the limit LF? You can't tell and I ain't gonna try and find out!:cool:

[gassed budgie]

From what I've been reading, in GA airplanes, Vno or the top of the green arc is a speed at which the aircraft is able to withstand up or downdrafts of up to 30 feet / second without over loading the plane


Most of the light aircraft we fly today were certified under the old CAR part 3 regs (pre '65). The certification criteria dictated that when operating in the green arc, the aircraft structure had to withstand an instantanious '50 per/sec vertical gust without bending anything. That's around 30 knots. I reckon if you happened hit a vertical gust of this magnitude whilst punching along at 160 kias in the 210, it'd certainly capture your attention quick smart. I've got absolutely no doubt one would be looking out the window at the wings rather suspiciously (mistakenly as it turns out).
When in the yellow arc by the way, the airframe has to be able to handle a '30 per/sec vertical gust, again without bending/breaking anything.

Another misconception that you quite often hear, is that it's OK to descend at cruise power in smooth air with the IAS in the yellow. Inncorrect.
The regs (CAR 3) state that the yellow arc is only for inadvertant excursions of airspeed . In other words, if you find yourself on the high side of Vno, get yourself and the aircraft back in the green arc on the ASI.


The C210 is deliberately limited by Cessna to avoid overstress in the un strutted wing/fuzelage attach area.
This has been the subject of debate for years but the end conclusion is that the way the wing attaches does warrant care in turbulent conditions.


The C210 was limited by Cessna (as was any other model manufactured by Cessna) to meet the requirements of CAR 3 under which the aircraft was certified. To say that it was hobbled by Cessna because the wing was strutless or because of the way that the wings attached to the fuselage is incorrect. The strutless wing easily met the requirements needed to gain certification under CAR 3.
The wing on the 210 when compared to say, an A36 or Saratoga/Lance, doesn't warrent any extra consideration other than the normal precautions that a pilot might take when operating in turbulent conditions.
The fact of the matter is, the spar carry through structure on the 210 is stronger the the strutted wing of the 206. So if you do happen the hit that 50' per/sec gust in your 210, relax.

As an aside, one of the strongest set of wings that Cessna ever put on aeroplane were strutless. These belonged to the 195 series. Because of a number of design considerations that were made at the prototype stage, the wing was overbuilt (not on purpose) i.e. it was heavier than it needed to be.
When Cessna tested the wings, they didn't break when they were supposed to. They went way, way past the point at which they were supposed to let go. So rest assured, when out driving in your 195, you'll break before the wings do!

[Oktas8]

das uber soldat, and makeithappencaptain,

That aeroplane did not crash because the pilot went ten or twenty knots too fast in turbulence. If you have read the report behind it, perhaps you might tell us what led to the crash. (Exceeded Va by 10 or 20kts in moderate turbulence on an otherwise fine day? Ha ha.)

There is a difference between going slightly too fast and going 50% too fast, or going into a mature thunderstorm. It's because I know that, that I spent years being allowed to test people. And seeing them, for example, do max rate turns above Va. Naughty naughty. But yet we didn't crash. No, of course I didn't condone it though.

If a pilot reading this forum goes away thinking that flying through moderate turbulence above Vb or Vra will break something, he will be surprised when he accidentally does it one day. Because there probably won't be anything to see to the casual eye - unless of course ten or a hundred other pilots have done so before him, or if he went up to Vne in moderate or severe turbulence! But it's still bad, because of fatigue and hidden parts that are damaged if only slightly. So even if there seems to be no damage, report it at least verbally to a friendly LAME who knows what look for.

Have you seen the slight wrinkling of an overstressed fuselage? It isn't obvious. Have you felt the excess play in a worn-out stabilator bearing? Again, not necessarily obvious.

That's the message I'm trying to say. Nothing to do with flight through thunderstorms.

[MakeItHappenCaptain]

Have you seen the slight wrinkling of an overstressed fuselage? It isn't obvious. Have you felt the excess play in a worn-out stabilator bearing? Again, not necessarily obvious.

All the more reason not to do it. How do you know previous pilots haven't gradually worn down that nice limit-ultimate margin? I'm not saying a 10 knot exceedance will bring you undone and I'm sure no-one will be "disappointed" the airframe didn't fail, but Va is set for a reason and to introduce a healthy fear/respect of exceeding this parameter is definitely not a bad thing imo.

I agree with using Va in lieu of Vb, as previously stated, the littlies don't have the same certification reqirememts.

My agreeing with Uber had nothing to do with the commander photo specifically, just not happy with the generalised understatement of what can happen. Worst case scenario, I know and no apologies for that, but it's the old/bold scenario that will keep you alive the longest. Remember the age of Australia's GA fleet.:ok:

[aileron_69]

If you are flying geophysical survey in a 210 then it alters the dynamics somewhat. Going high isnt an option, and if you slow down too much you can risk driving into the side of a hill.

Put your drink bottle on the seat next to you. If said drink bottle is regularly floating around the cabin, and you are also feeling those sickening big thumps every so often that are a bit painful, its time to go home....so go home!! The survey lines will still be there tomorrow to fly when hopefully it isnt so rough. Especially if it is my survey plane you are flying, they cost too much to fix!!!!

On another note, everybody worrying about the wings falling off may want to take a closer look at the tailplane of their 210. It will give up first you will find. My 210 has had its tail rebuilt 3 times now but the wing has only broken once.

[rutan around]

Aileron 69,
I'm curious. When you say your C210 tail has broken 3 times was it the horizontal stabilizer to fuselage (forward attach fittings) that failed and if so after the first failure did you have the doubler mod fitted ?
Cheers RA

[ForkTailedDrKiller]

The only catastrophic in-flight failure of a C210 that I can recall, occurred near Cloncurry back in the 70's. Wing failed at the flap/aileron junction, if I remember correctly.

Dr :8

[Capt Fathom]

C210 Cloncurry (http://www.atsb.gov.au/media/24622/197600023.pdf)

[rutan around]

There isn't enough information in the Accident Report to really determine what happened. However if the limited information available is accurate it appears this may have been a flutter event. I once heard an aircraft flutter and a sound a bit like a misfiring engine is a reasonable description. The witness statements that the aircraft had commenced a right turn do not fit the overloaded outboard section of wing failing in the downward mode scenario. If that scenario had occurred the right wing would be the broken one. Turning right would speed up the left wing and perhaps that was the straw that broke the camels back. C210's don't have a great flutter margin but it is of no concern providing it is flown inside the design envelope. There is an aileron beef up mod available. This was developed when people started playing with much more powerful engine installations such as turbines.
Cheers RA

[djpil]

The regs (CAR 3) state that the yellow arc is only for inadvertant excursions of airspeed I don't see that in CAR 3. (I am aware of a reg which states that a pilot must do what the AFM states.)

How many G's can Light, Moderate, and Severe turbulence produce based upon their prescribed FPMs?The standard equation for gust load factor:
http://adg.stanford.edu/aa241/structures/images/image5.gif
with: a = (dCL/da) - lift curve slope - try 5 for a simple calculation
Ue = equivalent gust velocity (in ft/sec)
Ve = equivalent airspeed (in knots)
Kg = gust alleviation factor - try 0.85 for a simple calculation
W/S is wing loading in lb/sq ft
(I hope my memory has worked for the "try" numbers, I haven't had any coffee this morning yet)

[aileron_69]

Rutan:

Its broken in different places each time. The forward attach fittings have broken, so have the rear. We do now have the doubler mod fitted. It also needed the rear 2 or 3 (cant remember how many) bulkheads replaced as they cracked. Was a rather expensive process. I would say part of the cause of the bulkhead damage would be directly related to the stinger on the tail.

Cheers
Aileron

[rioncentu]

The Cloncurry Incident report states:


"A rapid application of a large amount of right wing down aileron control at speeds in the vicinity of the normal cruising speed could produce torsional loading in the left wing in excess of the design strength of the wing and result in
wing failure consistent with that which occurred in this accident."


So what do we consider to be a "safe" amount of control deflection at speeds above Manouvring Speed?

[ForkTailedDrKiller]

Thanks Capt! I wasn't aware that there were witnesses.

Bit of a mystery really.

Happened around the time I first started flying 210's - gave considerable food for thought.

Dr :8

[MakeItHappenCaptain]

Its broken in different places each time. The forward attach fittings have broken, so have the rear. We do now have the doubler mod fitted. It also needed the rear 2 or 3 (cant remember how many) bulkheads replaced as they cracked. Was a rather expensive process. I would say part of the cause of the bulkhead damage would be directly related to the stinger on the tail.

Wasn't there an SB that came out recently as a result of a stinger equipped a/c with this damage?

[aileron_69]

Sure was, it was the rear attach point on the Horizontal Stab breaking, and that caused the stab to move, jammed the elevator, and nearly brought the aircraft down. When other operators checked their aircraft about half found the rear attach points cracked and needing replacement.

[aileron_69]

Just had this arrive from Cessna today regarding Spar cap inspections.
This could ground a few aircraft.

https://support.cessna.com/custsupt/contacts/pubs/ourpdf.pdf?as_id=37240

[ImaginedByGod]

Thanks for that link 69.

[rutan around]

For most readers of this thread I'm probably teaching my grandmother how to suck eggs with this C210 pre flight check to determine if the horizontal stabilizer to fuselage attachments are ok.
Grip the outboard end of horizontal stabilizer and push it up and down a few inches (fairly slowly.don't use excessive force.)

You should hear an oil canning noise as the skin flexes. This noise is ok
If you hear a crunchy or grating noise DON'T FLY.

If this test only prevents 1 accident it was worth boring those who already include it in their pre flight checks.

To recognize the difference between an oil canning noise and the dreaded crunchy noise I
recommend the following procedure.

1) Empty one aluminum beer can

2) Lightly squeeze and release the can several times between thumb and forefinger. That noise is oil canning or in this case beer canning.

3)Now using a screwdriver or knife rip and tear a break approximately half way round the circumference of the can. Grasp each end of the can and slightly rotate the ends back and forth in opposite directions. That is the crunchy "DON"T FLY" noise.

When Mrs RA politely inquired why I had just drunk 8 VBs I just as politely informed her that the recommended procedure would have to stand up to peer group review and one couldn't be too careful. The mower shed isn't all that cold and uncomfortable.

I recommend the above procedure to anyone unsure of the noises they should be listening out for whilst performing the essential horizontal stabilizer pre flight check.
Cheers RA

[ImaginedByGod]

I'll try that horizontal stabilizer test tomorrow......a few inches though? Doesn't that seem like a bit much?

[rutan around]

A few inches is probably a bit of an overestimate. (male problem) The few inches of movement I was referring to is the amount the whole aft end of the aircraft moves.( NOT the movement of the stabilizer tip relative to the fuselage. Anyway just move it enough so you hear the oil canning and know you are putting a bit of pressure on those critical attach brackets which unfortunately can't be seen.
Cheers RA

[Frank Arouet]

CPA E-ATIS

Volume 15 Issue 05

May 1, 2012



CESSNA CALLS FOR INSPECTION OF LOWER SPAR CAP ON CANTILEVER WING 210’s, FAA TO FOLLOW WITH AN IMMEDIATELY ADOPTED RULE AIRWORTHINESS DIRECTIVE



Friday April 27th Cessna issued Service Letter SEL-57-01 which calls out for a visual inspection of the first 20 inches of the lower spar cap on both wings of 210s with over 5,000 hours total time in service. On aircraft with more than 10,000 hours an external visual inspection must be done before further flight and an internal visual inspection within the next 5 hours. On aircraft with between 5,000 and 10,000 hours an internal visual inspection must be done within 25 hours. On all aircraft with more than 5,000 hours this internal visual inspection must be repeated every 100 hours or 12 months whichever occurs first.



Cessna made a presentation to the FAA’s Wichita Aircraft Certification Office (ACO) on Friday April 27th during which Cessna requested that the FAA issue an airworthiness directive. Cessna’s presentation so impressed the ACO that at a meeting on Monday April 30th they decided to issue an Immediately Adopted Rule (IAR) that puts the AD in effect with no comment or input from the public or industry until after the fact. This IAR process is supposed to be used only in cases where the threat to public safety is so severe as to preclude the FAA from using its normal rulemaking procedures.



Interestingly, according to the FAA not one cracked spar cap has been found to date on aircraft operated in the US.



So what brought this all about? Look to the Land Down Under. Australia’s Civil Aviation Safety Authority (CASA) is that country’s equivalent to the US’s FAA. CASA reported to Cessna and the FAA that they had reports of 7 incidents of spar cap cracks on Cessna 210s and that this problem was “common knowledge” in that country. The FAA looked around and could find no reports of spar cap cracks in the US but did find one from Canada. Meanwhile these reports had Cessna’s attention big time and they started writing a service bulletin to deal with it.



CPA first became aware of what was in the wind when we were provided a draft of Cessna’s service bulletin late the afternoon of Friday April 27th. A call to the FAA picked up that there was going to be a meeting on Monday April 30th to decide what action to take.



This is serious business and could have a profound effect on the 210 fleet and the value of the aircraft.



As this was a shot out of the blue for us, CPA staff had to get up to speed quickly. Tom Carr was already here in Santa Maria to teach a 210 class. Phil Kirkham of Coastal Valley Aviation was involved in the class as well. I called Paul New at Tennessee Aircraft and got him on board. Paul is more knowledgeable about the spar system on the 210 than anyone else as he repairs them. So I had a top team of people available to sort this issue out.



The first thing we determined was that none of us had seen or heard of cracks in the lower spar cap on the 210. On Sunday (Monday in Australia) I spoke with three repair stations in Australia, including the largest Cessna Service Center in the country, and none of them knew anything about it. So much for the problem being common knowledge.



Second thing we discovered is that the inspection cannot be carried out with a light and a mirror as called for in the Cessna service bulletin. You can see most of the cap with a light and a mirror but not all of the cap area called out for inspection. This is particularly true for aircraft with de-ice boots and/or avionics bays in the wings. Later we found out that the people at Cessna involved in writing the service bulletin hadn’t actually gone out and looked at a real 210 in this area, they were working from drawings and memory.



And what about those 7 reports in Australia? I searched 10 years of CASA Service Difficulty Reports and could not find a single reference to this. There also were no Australian ADs, Bulletins or Advisories. So how does anyone know about these 7 aircraft. On Sunday, their Monday, I placed a call to CASA and they actually called me back. It turns out that CASA has only two confirmed reports of spar cap cracks. These reports are very recent and apparently have not made their SDR listing yet. The aircraft involved had 15,000 hours and 5,600 hours.



It is the 5,600 hour aircraft that is causing all the knee jerk reaction by government agencies and Cessna. That is way to low a time for this sort of thing to occur, though at this time extenuating circumstances have not been found. However no one from CASA has looked at this aircraft. And what about the other 5 incidents in Australia? Well it seems as if somebody has recently mentioned these aircraft to CASA and now CASA is trying to find out more. So solid, verifiable cases? Only 2, not 7. Throw in the SDR from Canada and that makes 3. So it is 3 aircraft verified, not 8.



And what happened to these aircraft with cracked spar caps? Were the cracked spar caps thrown away? Cessna hasn’t sold a lower spar cap in 6 years. The Canadian aircraft did buy a new wing from Cessna, I am told.



Apparently the FAA and Cessna became aware of these cases in Australia about 10 days ago and have been running around like chickens with their heads cut off since. There are three verified incidents, no accidents, and no cases in the US. These cantilever wing Cessna 210s have been flying for 45 years without this problem rearing its ugly head, you would think we could take more than a few days to gather data and get this right.



First of all somebody knowledgeable needs to look at the 210L in Australia that had a spar cap failure at 5,600 hours (or 5,750 hours, they don’t seem quite able to pin that down). That number is so out of line that we have to be suspicious. Was the spar cap heat treat correct when it was originally manufactured? Was the spar assembled correctly at the factory? Was the aircraft equipped with tip tanks at any time (which would have greatly increased the stress on the lower spar cap)? Was corrosion involved?



The other two verified incidents are on aircraft with over 10,000 hours each, but Cessna’s SB and the impending AD subject a much larger portion of the fleet to onerous inspections because of this one airplane that hasn’t been very well scrutinized?



And here is another little twist. Australia changed their rules a few years ago and now requires their mechanics to abide by FAA issued ADs. CASA only issues a Australian AD if the FAA chooses to pass on issuing an AD on a subject that CASA thinks an AD should be issued on. Instead of rushing off to impose rules, without public input, that will affect 210s in the US where this problem has not been seen, perhaps the FAA should say to CASA, ‘We’d like to help you, bloke, but we need more data, particularly on the low time incident.”



We don’t know yet what the Immediately Adopted Rule AD is going to say, but it really shouldn’t include the reoccurring 100 hour or 12 months inspection called for in Cessna’s new SB. That is something that does not fall any where near the requirements for bypassing public input, and so far there appears to be no engineering data to support it.



Cessna’s SEL-57-01 requires that operators report the results of the inspections, cracks or no cracks, to Cessna. If the FAA is going to impose an Immediately Adopted Rule then the reports should come to the FAA, not Cessna, so that they will be available for public scrutiny. In fairness to Cessna, the factory has always been open about sharing information CPA has requested. However on an issue this big and important it is in everyone’s best interest, including Cessna’s, that there be transparency.



So, on to the inspection. Basically inspection panels are removed on the bottom skin of the aircraft to gain access to the wing spar assembly from the wing root at station 25.52 outboard 20 inches to station 45.00. This is the area where the Huck bolts sandwich the spar cap, spar fittings and spar web together. The spar cap is a tee shaped extrusion with the vertical portion of the tee fastened between the spar fittings and web. The wing skins are lap joint riveted to the cross of the tee.



The area to be inspected is the fore and aft flanges of the spar cap and as much of the vertical flange as can be seen. First the area has to be cleaned. Depending on the conditions the aircraft has been operated in this can range from blowing out with shop air to repeatedly brushing in Varsol and then blasting shop air.



Once clean the edge and face of the flange is visually inspected for cracks. Several of us tried doing this with a light and a mirror but weren’t real happy with what we could see. It became clear if the aircraft had avionics bays and/or deice boots a light and a mirror wasn’t going to cut it. We tried various optical devices with limited success. Then I found the perfect tool at, of all places, Harbor Freight. It is called a High Resolution Digital Inspection Camera with Recorder. Item 67980. On sale for $200. This little flexible ecoscope can fit about anywhere. It takes pictures and videos. It can be hooked up to a monitor or computer. But most importantly we could see all of the spar cap including sections of the vertical. The inspection should take an hour to two hours depending on how much cleaning has to be done. So the inspection shouldn’t be particularly a problem unless of course cracks are found.



This is a developing situation so you can expect change to occur. Right now if you have a high time 210 I think I would hold off until some of this gets sorted out. At this time there is no requirement that you have the inspection done though it will be mandated shortly by an Airworthiness Directive. It going to take Cessna a bit of time to straighten out their service bulletin and then the FAA a bit more time to promulgate their Airworthiness Directive. CPA staff believes when the time comes to get the inspection, it best be done by shops that are intimatelyfamiliar with the 210 and these sorts of inspections. CPA will keep you informed.



You can read and print Cessna Service Letter SEL-57-01 here (mhtml:{B39EE9F3-2420-4EFA-9500-3C893C85FAB8}mid://00000020/!x-usc:http://www.cessna.org/atis/1505/sel_57_01.pdf)



We are posting spar pictures provided by Paul New. Links below:



Photo 1 (mhtml:{B39EE9F3-2420-4EFA-9500-3C893C85FAB8}mid://00000020/!x-usc:http://www.cessna.org/atis/1505/210_spar_1.JPG)

Photo 2 (mhtml:{B39EE9F3-2420-4EFA-9500-3C893C85FAB8}mid://00000020/!x-usc:http://www.cessna.org/atis/1505/210_spar_3.JPG)

Photo 3 (mhtml:{B39EE9F3-2420-4EFA-9500-3C893C85FAB8}mid://00000020/!x-usc:http://www.cessna.org/atis/1505/210_spar_4.JPG)

Photo 4 (mhtml:{B39EE9F3-2420-4EFA-9500-3C893C85FAB8}mid://00000020/!x-usc:http://www.cessna.org/atis/1505/210_spar_5.JPG)

Photo 5 (mhtml:{B39EE9F3-2420-4EFA-9500-3C893C85FAB8}mid://00000020/!x-usc:http://www.cessna.org/atis/1505/210_spar_6.JPG)

Photo 6 (mhtml:{B39EE9F3-2420-4EFA-9500-3C893C85FAB8}mid://00000020/!x-usc:http://www.cessna.org/atis/1505/210_spar_7.JPG)

Photo 7 (mhtml:{B39EE9F3-2420-4EFA-9500-3C893C85FAB8}mid://00000020/!x-usc:http://www.cessna.org/atis/1505/210_spar_8.JPG)

Photo 8 (mhtml:{B39EE9F3-2420-4EFA-9500-3C893C85FAB8}mid://00000020/!x-usc:http://www.cessna.org/atis/1505/210_spar_9.JPG)

Photo 9 (mhtml:{B39EE9F3-2420-4EFA-9500-3C893C85FAB8}mid://00000020/!x-usc:http://www.cessna.org/atis/1505/210_spar_11.JPG)

Photo 10 (mhtml:{B39EE9F3-2420-4EFA-9500-3C893C85FAB8}mid://00000020/!x-usc:http://www.cessna.org/atis/1505/210_spar_12.JPG)

Photo 11 (mhtml:{B39EE9F3-2420-4EFA-9500-3C893C85FAB8}mid://00000020/!x-usc:http://www.cessna.org/atis/1505/210_spar_13.JPG)

[Frank Arouet]

CPA E-ATIS

Volume 15 Issue 06

May 2, 2012



UPDATE ON 210 SPAR CAP ISSUE



Well, when you stir the pot things happen. An update on the 210 wing spar cap service bulletin.



-Turns out Cessna has not asked for an airworthiness directive. I was told that by someone at the factory that was not in the meeting. Cessna left the action decision solely to the FAA.



-Some felt that when I said people with high time aircraft should hold off getting an inspection until this gets sorted out, that I meant it ain’t that big a deal wait awhile. What I meant was hold off until Cessna gets their service bulletin cleaned up and with the right information in it. I expect that will take less than a week.



-The hours on the low time airplane in Australia have been confirmed at 5750 hrs not 5600.



-Two more aircraft in Australia have been verified to have had cracked spar caps. One is a 12,000 hour 210L and the other is 9,000 hour 210M owned by a CPA member.



-The FAA has told us that they are requesting further information from CASA on the 5750 hour aircraft. As they say in Australia – Good on ya, mate.



-CPA has provided Cessna and the FAA a list of areas we think the service bulletin needs to be corrected, clarified and improved.



-Paul New at Tennessee Aircraft has now done 5 inspections, Phil Kirkham at Coastal Valley had done one (actually kind of more than that as he was looking at spar caps with us all weekend). No cracks found so far. If someone feels they want the inspection right now, either one of those shops would be good places to have it done. And Yingling in Wichita can certainly go on the list.



-It's becoming clear that if the aircraft does not have boots or wing avionics bays the inspection can be done with a light and a mirror. If it has either of those a thin flexible borescope will be needed.



That’s the update as of Wednesday May 2nd.

[das Uber Soldat]

das uber soldat, and makeithappencaptain,

That aeroplane did not crash because the pilot went ten or twenty knots too fast in turbulence. If you have read the report behind it, perhaps you might tell us what led to the crash. (Exceeded Va by 10 or 20kts in moderate turbulence on an otherwise fine day? Ha ha.)


Alright mate, you've lost me. As someone with 500 hours on the shrike I took a special interest in that report. From its findings, TAS at the time of failure was 165 kts, which coincidently is exactly flight plan TAS so a credible figure.M

At 7000 ft 3 deg OAT, thats an IAS of 145 KIAS. Published Va for the shrike is 141 KIAS. The thing was 400 kg below MTOW so reduce that to 131 kts, making the a/c at best estimate, 14 KIAS over Va at the point of failure.

"That aeroplane did not crash because the pilot went ten or twenty knots too fast in turbulence." - The final report suggests this is exactly what happened.

So Yeh, you've lost me.

[aileron_69]

Two more aircraft in Australia have been verified to have had cracked spar caps. One is a 12,000 hour 210L and the other is 9,000 hour 210M owned by a CPA member.


Either there have been 3 more aircraft in Australia or the 210M (mine) actually had 14500 hours when the spar cap cracked. Had an L a few years back that did the same thing around 13000hrs. Its not a new thing to start happening. Fortunately opposite wings so we could replace the damaged wings on both planes with both sets. Cessna say they havent sold and spar caps in the past few years. That is because they cost so damn much, and the massive cost in labour to replace them, it is just quicker, easier, and cheaper to put whole new wings on the aircraft to get it back flying.

[flyinwithme99]

Please let it be noted that the notice Cessna published is a "Service Letter" not a "Service Bulletin" which I myself found rather strange because of the subject matter and importance which Cessna made this alert.

Thank you for the referral by the way. Yingling is your one stop shop for Cessna products.

[flyinwithme99]

Here is an explaination from Cessna concerning the issuance of Service Bulletins and Service Letters

Q: What is the difference between a Service Bulletin and a Service Letter.
A: Service Bulletins are technical documents that provide parts, instructions and approval for incorporation of an installation, modification or repair to a specific Cessna airplane by model and unit number. They are used to announce special product inspection criteria and modifications, revised maintenance information, operational information which is intended to assist in improving aircraft safety, reliability, durability, or performance.
There are four compliance categories for service bulletins and are defined as follows:
A. MANDATORY. Cessna's compliance level for a service document that must be accomplished for continued airworthiness under 14 CFR 43.13.

B. RECOMMENDED. Cessna's compliance level for a service document that modifies or changes and airplane system that are intended to improve dispatch reliability which should be accomplished within the specified time requirements.

C. DISCRETIONARY. Cessna's compliance level for a service document that modifies or changes and airplane system that is intended to improve dispatch reliability which can be accomplished at the discretion of the airplane owner.

D. OPTIONAL. Cessna's compliance level for a service document that installs, upgrades components, systems, or the airframe at the customer's request. Optional service bulletins are accomplished at the customer's expense.
Service Letters provide Information important to the maintenance and operation of airplanes. While Service letters might provide instructions on how to accomplish a task they do not provide parts and approval for the work accomplished.</STRONG>

[rutan around]

Aileron 69
I understand you do a lot of low level often rough air flying. Referring to those two 210s,which suffered spar cap failures at similar airframe hours could you give an estimate of the percentage of each aircrafts TT spent in rough air. I realize you probably didn't operate them from new but a rough estimate might be educational for other C210 owners. I know some of the Northern Territory mail planes have around 30,000 hours and I haven't heard of spar cap problems. They have rough air but would mostly fly above it. It's just the short sector routes that would be all rough.
Cheers RA

[aileron_69]

Gday Rutan,
Both the 210s that had spar cap cracks had long range flint tip tanks on them and probably spent at least half of their 14000 hours below 300feet in the 'rough stuff.' Its a pretty hard life for the old girls and the tip tanks dont really help.

[ImaginedByGod]

Hey FA, the links don't work.....

[Capt Fathom]

Links don't work....


mhtml:{B39EE9F3-2420-4EFA-9500-3C893C85FAB8}mid://00000020/!x-usc:http://www.cessna.org/atis/1505/210_spar_1.JPG


You need to delete all that rubbish in front of..... http://www.cessna.org/atis/1505/210_spar_1.JPG

[rutan around]

Aileron 69
Thanks mate you've cheered me up. My 210 although it has Flint tanks is only a pup at just over 10,000 hours. Also it spends most of it's time in smooth air. It would appear that what's good for me is also good for the plane. I checked with a big 210 operator in WA & NT and they have had no problems even on their 30,000 hr units. My contact said they fly high whenever they can and their fleet doesn't have tip tanks.
Cheers RA

[ImaginedByGod]

Thanks Captain :O

@Rutan, I tried your horizontal stabilizer trick on 2 different planes and it looks and sounds like the aircraft skin is just moving and warping. no grossly disturbing knife to the can sound.......

[rutan around]

RE C210 SPAR CAP PROBLEM
I spoke to a Cessna Pilots Assn. technical adviser this morning ( Wed 9-5-12 ) They are still seeking information regarding the supposed spar cap failure on a 210 with only 5,750 hrs I'm not sure they even have its' VH call sign. They would very much like lots of information about this aircraft. Was it ever determined what caused this apparently one off low time failure? How was it operated over its' lifetime prior to failure? Perhaps it tangled with a thunder storm or perhaps the operator had a penchant for aerobatics. Perhaps it was a manufacturing fault. This information is urgently needed to determine the direction of further action. So far in US a few hundred have now been checked and none have been found with cracks.
Anyone out there with information about any 210 spar cap failure please share it with us so appropriate action can be taken. Aileron 69 your information was appreciated.
Cheers RA

[AC103]

From the Manual of Aviation Meterology, chapter on Turbulence

Light = 300-1199 fpm
Moderate = 1200-2099 fpm
Severe = 2100-2999 fpm
Extreme = >3000fpm



Caution resurrection... does anyone know where else this data is defined? I can't seem to find it in the RGL https://rgl.faa.gov/ or the WMO library https://library.wmo.int/ or via ICAO?

[AC103]

OK I found this from the WMO Technical Regulations, Volume I - General Meteorological Standards and Recommended Practices
https://library.wmo.int/doc_num.php?explnum_id=9359

https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/720x520/convetive_turblence_7872f099b7b255484639f20c3dddb2a550a3e749 .png

Does anyone know of any regs for instance in Aircraft Certification that lines up with this?

[djpil]

This probably won't answer your question but some good background for transport category here https://www.faa.gov/regulations_policies/rulemaking/committees/documents/media/TAEladT5-06101994.pdf