Why can't engines be swapped?

tech77jp · 06-16-2003, 01:27 PM

In light of Air Canada's announcement to retire its few 747-400s, I was wondering - why can't GE engines be swapped for RR engines, etc. on commercial aircraft? I imagine that part of the reason for replacing these airliners with A340-600s is because of the high maintenance costs associated with a mixed fleet, but I never hear about airlines retrofitting turbofans of one manufacturer onto an existing commercial aircraft. Why can't this be done (wouldn't it lower servicing costs)?

I imagine there would need to be some reprogramming with the avionics to become compatible with the slightly different specifications, but the basic airframe is the same, right?

ZX1100F1 · 06-16-2003, 07:20 PM

There are so many items that are engine brand specific when building an airliner that I honestly don’t know were to begin.
The pylon itself is specific.
The fuel lines and engine feed pumps are specific.
The engine FADEC controls and wiring are specific all the up to the cockpit and avionics compartments.
The engine accessories have variances and changes to the aircraft upstream must be made to accommodate for this.
The weight and balance of the aircraft is changed and would necessitate re-certification.

This is just scraping the surface, the most common engine swapping was done on the DC-8‘s were they replaced the old JT-3’s (noisy and thirsty) with modern CFM56’s. There was a kit that was engineered and manufactured to make this swap easier but it was still a very expensive undertaking.
The benefits to swapping engine makes on a 747-400 are going to be far outweighed by the cost to make the swap, I am not aware of any 747-400 that has had its motors swapped.
This is the same kind of logic as: Spending $5,000 for a diesel engine in your ¾ ton truck because diesel fuel is a penny cheaper per gallon.
Doesn’t make much sense.

06-16-2003, 01:27 PM	#1
tech77jp Senior Collector Join Date: Mar 2002 Location: Osaka, Japan Posts: 435	Why can't engines be swapped? In light of Air Canada's announcement to retire its few 747-400s, I was wondering - why can't GE engines be swapped for RR engines, etc. on commercial aircraft? I imagine that part of the reason for replacing these airliners with A340-600s is because of the high maintenance costs associated with a mixed fleet, but I never hear about airlines retrofitting turbofans of one manufacturer onto an existing commercial aircraft. Why can't this be done (wouldn't it lower servicing costs)? I imagine there would need to be some reprogramming with the avionics to become compatible with the slightly different specifications, but the basic airframe is the same, right? __________________ "Everything good in life is either illegal, immoral, or fattening." - Murphy http://www.soaringcapture.tk/

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06-16-2003, 07:20 PM	#2
ZX1100F1 Buford T. Justice Join Date: Sep 1999 Posts: 2,004	There are so many items that are engine brand specific when building an airliner that I honestly don’t know were to begin. The pylon itself is specific. The fuel lines and engine feed pumps are specific. The engine FADEC controls and wiring are specific all the up to the cockpit and avionics compartments. The engine accessories have variances and changes to the aircraft upstream must be made to accommodate for this. The weight and balance of the aircraft is changed and would necessitate re-certification. This is just scraping the surface, the most common engine swapping was done on the DC-8‘s were they replaced the old JT-3’s (noisy and thirsty) with modern CFM56’s. There was a kit that was engineered and manufactured to make this swap easier but it was still a very expensive undertaking. The benefits to swapping engine makes on a 747-400 are going to be far outweighed by the cost to make the swap, I am not aware of any 747-400 that has had its motors swapped. This is the same kind of logic as: Spending $5,000 for a diesel engine in your ¾ ton truck because diesel fuel is a penny cheaper per gallon. Doesn’t make much sense.