STC Vs EO

[Guptar]

I'm quite familiar on the use of EO(ngineering Order), where a modification is being done to an aircraft, drawings are ade up and a CASA Engineer reviews the propsed mod and gives it the yay or nay.

So where is the line in the sand where a proposed mod is too lage in scope and an STC is required. How is that line defined.

Cheers.

[Air Ace]

I think you will find an EQ from a CAR35 engineer applies to a specific aircraft, nominated by registration and/or serial number.

An STC applies to a modifications carried out to all aircraft of a specific type or model.

But I may be wrong........

[LeadSled]

Folks,
The real difference is you can sell an STC to somebody else. As long as it remains in the fleet, an EO will do for an internally developed mod.
Tootle pip!!

[Guptar]

So what happens if the aircraft is sold, does the EO go along with the aircraft or or does the new owner have to re apply fo the EO.

An EO is used for smaller mods, but can it be applied to something majou like extra fuel tank installation etc.

[Bendo]

We have a large hole cut in the floor of our U206 - we got an EO for that. As Air Ace correctly stated, that approval is for our 206 only. We can't restore the aircraft to its original condition, yes the CAR 35 approval will remain with the aircraft.

If we wanted to install our sensor pack to a fleet of 3 aircraft, we would still just get CAR 35 EO's for all of them based on the first one we did.

Every aircraft type is issued with a Type Certificate - that is the final stage of the aircraft certification stage. A supplemental type certificate is issued to certify that with XYZ modification installed, the aircraft still meets certification criteria. A good example are the VG kits and winglets for Chieftains or RAM-series upgrades for Cessna twins.

If we were the Australian agents for these sensor units, we might get a Supplemental Type Cert because it would be easier than a one-off EO for each aircraft - but we would need to get a STC for each aircraft type that the gear could be installed in and THAT would be a horrendous, expensive nightmare. I expect you would need to do flight testing and produce flight manual supplements for an STC. That's fine when you have designed a VG kit for a specific type (eg Chieftain) but not otherwise :uhoh:

[john_tullamarine]

Air Ace and Bendo have the basics of the story.

(a) EO (by whatever name) looks at the particular aircraft (singular or plural) nominated in the control documentation. The approving design signatory (usually an Industry chap .. CAR 35 authorised person) is certifying that the mod is OK for THOSE particular aircraft only. This certification addresses any other mods etc. which may already have been incorporated. There MAY be a problem if the aircraft is exported as one is relying on the next authority's acceptance of the EO.

(b) STC (generally) looks at a larger range of aircraft (as nominated) and makes a similar certification in respect of the STANDARD OEM build aircraft. It is necessary for appropriate folk to check that a particular aircraft into which the STC mod is proposed to be installed doesn't have any individual mods (typically via EO) which could compromise the STC mod. This check is done either by design engineers (CAR 35 in Oz) or the installing agency/maintainer