Intermixed Engines Operations

[WannEDbe]

Hi all.
I'm at last in the right place!
Thanks for the welcome!

I'll start with a tricky one - from my layman's optic though.

Are intermixed engines operations a common practice in the US? Worldwide?
Under whose approval or regulations?
Manufacturers?
Do airplanes have built in provitions for this conditions?
Experimental? On active passanger carriers?
Heavy burden to count the Q's you experts surely would dig out.
One last thought: might it be common practice in some forgoten regions far from aviation regulation agencies/authorities?

Thanks anticipated.

WannEDbe

[sevenstrokeroll]

we mixed JT8D 7's an d 9's all the time on the DC9...slight pilot adustment and off you go...set slightly different power

mind you, its easier to have two of the same engines

[411A]

In the distant past, I have operated the L1011 with engine intermix, IE: -200 aircraft (two RB.211-524B02 and one -22B engines).
-22B (lower thrust) procedures are used on all three engines, reduced second segment climb performance, lower enroute altitude capability, and the engine intermix was allowed for only thirty days, by the regulatory authority.

All in all, a pain.

[WannEDbe]

sevenstrokeroll

[quote]
we mixed JT8D 7's an d 9's all the time on the DC9...slight pilot adustment and off you go...set slightly different power


This is a good start. The legal issue is still pending.
And yes, easier to have them paired and surely more cost effetive.

[acebaxter]

There are no legal issues at all. It is all allowed per the AFM on the DC-9.

[JammedStab]

Intermixed -15 and -17 on the 727. We were not allowed to do reduced thrust takeoffs with intermix. A bit vague now but I believe the reduced thrust was based on setting N1's for us and with intermix, they would be different values for different models.

[Dan Winterland]

Done it on 747-400s with CFM6s and FADEC. You have to change the engine control card (whatever that is) for the relevant engine position and the FADEC did the rest, apart from using the performance charts for the lower rated engine.

[sevenstrokeroll]

it seems to me that I have also done an intermix on the 737-200 (also JT8D)...doable but I didn't like it.

[aviatorhi]

Part of the "Super 27" conversion, -217s outboard and one -15 or -17 in the middle, going empty with a flaps 5 takeoff makes for a rocket ship.

[MarkerInbound]

We'd have intermixs on 727s at times. Boeing and the FAA were both happy. As I recall, it was only 7s and 9s, no 15s and lower. We'd do all the performance numbers based on -7 and set -7 EPRs across the board. As Jammed Stab said, no reduced thrust (some folks think a -7 is reduced thrust anyway.)

[HazelNuts39]

Originally Posted by WannEDbe

Under whose approval or regulations? Manufacturers?

Intermix must be approved under the airworthiness certification of the airplane. The beginning of the chain of approval is usually the manufacturer, who applies for it under the Type Certificate, and covers it in the Airplane Flight Manual, which is 'attached' to the airworthiness certificate of the individual airplane. The applicable regulations are, in principle, those of the state of registry of the airplane, whose authority issues the CofA. In practice, in most cases the state of registry accepts the regulation applicable in the state of manufacture as being equivalent to its own.

regards,
HN39

[mcdhu]

Also true for the A320 Series. FCOM 2.4.45 Ps 1-3 gives details of permissible intermix operations between CFM 56 SAC/DAC/TI engines.

[PappyJ]

Same on the A330's

[JammedStab]

Question for the fellows who have done intermix with non-JT8D engines.... Were you allowed to do reduced thrust ops?

[WannEDbe]

HN39.

Thanks.

My queries have been answered sufficiently. I trust all "big leaguers" have the capability for engine intermixing. And your post definitely shuts out all doubts as to the legitimacy of the procedures

Regards
WannEDbe.

[Mad (Flt) Scientist]

Originally Posted by JammedStab

Question for the fellows who have done intermix with non-JT8D engines.... Were you allowed to do reduced thrust ops?

Not mentioned above, but there are intermix options for various CF34 variants on the Bombardier CRJs, and reduced thrust takeoffs are I believe still permitted when intermixing; I can't recall any prohibition about it.

[pablodonosoi]

question -15 and -9 intermix

Hi my name is Pablo and I work IME Fae in Ecuador, we have a 727 100 , actually it has 2 jt8d-9 and we have a -15 so in the AMM of Boeing shows that there is possible make the intermix so is it really possible or not.
Thanks.for your attention