Cessna SID

[DavidWeston]

I've just heard that, as an owner of an 'ageing' Cessna 172, we are subject to a new regime of maintenance which may or may not involve a full check of things like struts, spars and prop.

Does anyone have any detailed info on this, or are is maintenance organisation taking advantage of us?

[Shunter]

That's called an annual isn't it?

[stevef]

I've only heard of Cessna Supplemental Inspection Documents being issued for certain twins although my ears could be out of date. I'm pretty certain a SID inspection for a simple single shouldn't exceed what a competent AMO would carry out on an Annual inspection, as Shunter suggests.

[Mike Cross]

You might find this (http://www.faa.gov/aircraft/air_cert/design_approvals/small_airplanes/cos/aging_aircraft/media/aging_aircraft_best_practices.pdf) of interest.

[DavidWeston]

Thanks for this

I should have said that our MO was saying that the new regime required us to have our prop overhauled, not just checked.

[A and C]

I would guess that you are being caught up in the general tightening of the rules by the CAA and propeller inspections are part of this.

I am guessing that you have a McCauley prop on your Cessna, these are subject to overhaul at six years or 2000 hrs. These times have over the past years been overlooked by a lot of smaller maintenance companys who used "engineers judgement" on such items.

Unfortunatly with pepole only too willing to rush to the legal action over the slightest thing so common sence has left the building and the CAA have no option but to tighten up on things that they had not been so hot on.

[DavidWeston]

Sounds about right, but why does this matter for Cessnas and not PA28s.
Surely for a fixed-pitch prop either all or none should need to be checked - oops shouldn't give the Belgrano any ideas

[smarthawke]

Sensenich have a similar 'overhaul' period with their fixed pitch propeller as McCauley. It is a manufacturers Service Bulletin and therefore not mandatory.

Sensenich SB:

http://www.sensenich.com/service_r17.htm

If your aircraft is maintained to LAMS or LAMP then the owner and engineer should decide whether a specific SB has to be complied with to ensure the continued safe operation and reliability of the aircraft.

If it is called up in the aircraft Service Manual then it has to be complied with (as with anything when on LAMS or LAMP, you have to abide by the SM as well as the schedule). On a PA28 the SM prop life is 2000 hours and no calendar time IIRC - as per the Sensenich SB.

Unfortuantely, many engineers have spent check after check attacking the blade leading edges with a file, then they misinterpret the legal requirements and start sending FP props away every Annual and most of them fail because of the blade dimensions! If they weren't quite so harsh on the props in the first place they would be fine.

Remember though, that a new prop will give a noticeable performance gain over a knackered old one. Personally, I'd spend the overhaul costs on a new prop when it really needs doing, you never get the same improvement with an 'overhaul'.

[ericferret]

Next on the list will be the Airborne CC211 vacuum pump. Page 22 of the latest GASIL states that Parker SL 58A lifes the pump at 6 years or 500 hours.

So you can expect your maintenance organisations to be trying to ping you for a pump change.

My understanding is that you should comply with the airframe manufacturers maintenance instructions.

For a Cessna 100 series aircraft the maintenance program says overhaul the engine accessories at engine overhaul. As they do not specify anything other than light maintenance for the propeller (fixed pitch) then it would be at the eng overhaul or 10 years which is the standard Lycoming calendar overhaul period. Not sure about Continental.

I suspect that we are going to see more of this. I would recommend in the first place asking your maintenance organisation to show you the relevent documentation and ask them to demonstrate why it is mandatory. Remember there is money to be made out of you.

Service bulletins and letters are normally only mandatory when backed up by an AD. As an example the Bell 47 maintenance manual was frozen years ago and the CAA issued an AD to say that any life or overhaul periods changed by an SB/SL were to be considered mandatory.

[DavidWeston]

Thanks Guys - that is good stuff. I'll be taking this up with our engineers on Tuesday

[A and C]

As Smarthawk points out the inspections depend on a number of factors.

The Vac pump thing in the latest GASIL is very intresting, with he CAA stating that the Parker built pump has a life of 500 hours/ 6 years, I note that this is a recomendation but GASIL seems to be taking the line that this is a hard life.

So what to do? there are three optons in this case

1 Fit the Parker pump and live with the hard life.
2 Fit a Rapco pump that has a vane inspection window and inspect the pump untill it reaches "life"
3 Fit an Airwolf pump that has a 2000 hour life and change it with the engine.
4 Run pump untill it fails and keep up your limited panel skills ready for the failure.

From looking at my records punp failure seems to happen at about 750 hours so my recomendation is that the Parker "life" is a bit conservative and so I would change the pump at the nearest maintenance check to the 700 hour point, this way you are unlikely to have a pump failure "downroute" that would costs more than having your regular maintenance company fit a new pump at a maintenance check when half the work to change the pump is already included in the price of the check.

[smarthawke]

Totally agree with you ericferret, the Piper PA28 service Manual states the vac pump should be changed at 1000 hrs OR at engine overhaul - it doesn't say whatever occurs first. I've known vac pumps fail within 50hrs from fitment.

If you maintain your aircraft to LAMS or LAMP then you have to abide by this, the airframe manufacturers servicing procedures and ADs, nothing else is mandatory.

I know companies that change privately owned aircraft vac pumps, overhaul FP props and carry out 500hr magneto inspections but not on their own fleet of training aircraft.

500hr magneto inspections are another good one. My CAA surveyor gave me a hard time for not doing them and implied that they were mandatory - till I pointed out they were not. Again the Piper SM, for instance is 'or change at engine overhaul'. I asked them for statistical evidence to prove that 500hr mag inspections made them last longer which he must have to insist that I do it - I'm still waiting 4 months on. He cited a case of a Mooney accident which suffered (single drive, dual mag) mag failure - I politely pointed out that the tragic, fatal accident occurred during the second take-off after the mag had been off for a 500hr inspection....

Minor point, in Lycoming Service Intruction 1009AS that engines should be overhauled in their twelfth year, not tenth if they haven't reached TBO first.

Another interesting bit in the latest GASIL highlights a statement in LAMS and LAMP in the 'how to do a Check A' section about turning engines over or running them during periods of inactivity due to say cruddy weather. LAMS says:

"If the aeroplane has not been regularly used, ensure before resumption of flying that:
a) either (i) the engine has been turned weekly or run fortnightly; or
(ii) the manufacturer’s recommendations have been complied with;"

Many will read the GASIL and and think that (i) might be good advice but goes against what Lycoming specifically say in their Service Letter L180B concerning periods of inactivity (and Ltycoming are the most common light aircraft engine in use):

"Pulling engines through by hand when the aircraft is not run or flown for a week or so is not recommended. Pulling the engine through by hand prior to start or to minimize rust and corrosion does more harm than good. The cylinder walls, piston, rings, cam and cam follower only receive splash and vapor lubrication. When the prop is pulled through by hand, the rings wipe oil from cylinder walls. The cam load created by the valve train wipes oil off the cam and followers. After two or three times of pulling the engine through by hand without engine starts, the cylinders, cam and followers are left without a proper oil film. Starting engines without proper lubrication can cause scuffing and scoring of parts resulting in excessive wear."

As for running, you need to fly the machine to get the engine hot enough to boil off any water/moisture, ground running isn't sufficiaent. SL180B again:

"Engine temperature and length of operating time are very important in controlling rust and corrosion. The desired flight time for air cooled engines is at least one continuous hour at oil temperatures of 165°F to 200°F at intervals not to exceed 30 days, depending on location and storage conditions. This one hour does not include taxi, take-off and landing time. If recommended oil temperatures are not obtainable, contact aircraft manufacturer for availability of oil cooler winterization plates."

Hopefully it might not snow tomorrow and I can go fly my machine and burn the water off!

PS I don't think the AAIB bulletin concerning the fatal Arrow accident which started off the vac pump comments has actually been releared into the public domain, contrary to what is said in the GASIL.

[ericferret]

Interestingly vacuum pump lives also seem to depend on installation. A pump vertically mounted in a 150 will probably last twice as long as one that is horizontally mounted.

The reason seems to be that gravity and rotational forces are acting in different directions on a 150, whereas the forces combine in a horizontal pump. As well as a light vacuum load.

Our last pump did over 14 years old and 1200 hours. Why would I have wanted to remove it at 6 years/500? It was a Rapco reconditioned pump. We only changed it because I was getting concerned about it's age. I stripped it and found out to my chagrin that there was virtually no wear evident

What about all those vacuum pumps with NO OVERHAUL embossed on them !!!!!!!!!! Buy a new one (from us of course)!!!!!!!!!

It is important to realise that the American legal system is a big driver in the excessively conservative lives placed on some items.

A number of years ago we were attempting to measure pitting wear on an R22 main rotor blade spindle. The max limit was one thousandth of an inch, almost impossible to measure in the field.

I suggested to the Robinson factory rep that this limit was drawn up by their legal department not their engineering department following a spindle failure. He didn't deny it.

[jxk]

SIDs were/are being introduced for all aircraft types as a result (probably) of the move to ARCs (Annual Review Certificates). Your MO should add a CAP543 (blue pages) to your log-book file indicating time-lifed items. An example of this are the flexible brake-hoses which should be changed at the wheel and pedal ends every 2 years (recommend replacing with Teflon) .
Incidentally, you now only pay for ARC when it submitted and for a 172 it currently £108.00.