View Full Version : What does it cost when you "firewall" an engine?
To start with - this is not an effrot to make pilots consider whether or not to Firewall and engine based on costs - when you need it you need it !!
Nevertheless - you go out, encouter a serious windshear on TO - and firewall the engine - and of course - write it up. Did you just buy the higher rated engine? Do they check the FADMS download and Pro Rate the info for Maintenance cost? Do they let you off the hook - Maintenance cost wise - if it was for short duration?
How do it know?
LK
lomapaseo
8th Mar 2004, 21:57
The maintenance manual typically contains instructions based on EGT level and RPM level as well as other deleterious effects like bangs pops and booms.
In the immediate sense there would be no additional maintenance costs.
The engineers would only have to look at the engines if you also reported an EGT or N1/N2 exceedance. Even then if the exceedance was small it is likely there would be no action required IAW the MM.
It is remotely possible that the overhaul life of the engine would be slightly reduced
The only engine I am aware off in which full power results in increased maintenance costs in the shorter term, is the V2500 fitted to the airbus. In this case if BUMP is used then it must be logged as the type is only allowed a certain number of BUMP take offs. This option is used on short fields and increases the turbine case cooling air to reduce turbine tip clearances and so increase engine efficiency. At the same time however, the blade tips tend to rub the casing thus reducing engine life.
According to my powerplant engineering Dept., it depends on what the peak temperature was and the duration of the overtemp (or overspeed). It can run anywhere from an inspection to a replacement.
LOKE,
If you fire wall an NG aircraft you get the maximium thrust for that motor,ie if the CDU Ident page shows you have the following;
CFM56-7b18=19500lbs
CFM56-7b20=20600lbs
CFM56-7b22=22700lbs
CFM56-7b24=24200lbs
CFM56-7b26=26400lbs
CFM56-7b27=27300lbs of thrust at the "firewall".
Take off power settings are only allowed for 5min,Max continous for 10min as per the AMM however you can exceed these provided you DO NOT exceed the 925c EGT limit,exceed the EGT limit and you are dependant upon the amount of temp & time spend in exceedance as to whether you inspect/repair/replace the engine.
You can only buy an up-rate for you engine by purchasing the software disks to reprogram the EEC for the new parameters,change the engine ident plug and provided you also have the correct HMU/fuelpump package as there is service bulletins listing the requirements.
The FDAMS are checked daily and are used for trend monitoring/ETOPS reliability data.The FDAMS takes a "snap shot" of all engine parameters at Takeoff,Stable cruise,and postflight .At the company i work for,All this data is sent to CFMI in the USA who track the data and advise the operator of any major problems upon discovery,reliability reports are sent regularly.
Phil Squares
9th Mar 2004, 12:37
Ok, I show my ingnorance. To answer the question, it depends on what engine you have, IE, FADEC/EEC or conventional fuel control unit.
On the older technology engines, if you "firewalled" an engine you ran the risk of over boosting the engine exceeding engine limitations and all the like. You would then have to write up the exceedance and MX would go into their books and look at the exceedances. You could in fact overtemp the engine to the point where it would have to be removed.
On the new technology engines, "theoritically" firewall gives you max epr/n1 for the existing conditions. For example on the P&W 4000, with the eec functioning normally, your max thrust is n1 limited. There is protection for overboosting, over speed and overtemp. As long as nothing was exceeded you don't have to write anything up.
Hope that helps.
:ok:
White Knight
9th Mar 2004, 22:43
If you don't firewall it when you NEED it you could end up hitting something hard - a la PALM 90. A whole aeroplane is a lot more costly than engine maintenance.
If in DOUBT, USE IT..........
Just to clarify, I definitely did not start this thread to elicit reasons why NOT to firewall engines when needed.
I'm reminded of a story of - I believe it was a military transport - where an A/C departed at MGTW and had a catastrophic engine failure which threw parts into the adjacent engine causing it to fail as well. Demonstrating incredible airmanship and judicious use of flaps and of course firewalling the remaining 2 engines the crew managed to bring it around for a landing.
The 2 remaining engines were dripping oil and obviously wasted. In the inevitable hearing, a maintenance officer pointed out that the 2 good engines were ruined and why did the pilot firewall them - he said - 'cause there was no way to get any more power out of them.
Good on 'em.
LK
Midland Maniac
11th Mar 2004, 00:14
are you talking about turbo-jet a/c or turbo prop??
If you firewall the engines on the PW123a (dash8 300) then it costs a hell of a lot of money, as torque can exceed 199%. This means that the engines have to be replaced as it damages the turbine blades. Not so bad on the PW150a (Dash8 Q400) as it is goverened by FADEC and will only give something like 117% of MTOP (don't quote me on the exact figures).
As a turbo-prop driver I could not comment on the effects on by-pass turbofans...
MM
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