Crack in the tail pipe
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Crack in the tail pipe
This is about a 'tail pipe' damage that occurred in a medium lift twin engined helicopter. This component is not the exhaust pipe of the engine, but a part of helicopter airframe and is positioned at the end of engine exhaust to facilitate smooth outflow of the exhaust gases. In fact it is a rolled, welded metal sheet for the purpose.
Now the meat part.
There was a one inch crack detected at the end of this pipe during a turn around servicing (the welding had given away). The discussion was "How bad things would get if the helicopter was flown back to the repair depot with the known fault still existing". Though legally I agree that it cannot be a good decision, nevertheless following implications were considered, had the decision to fly back to repair depot was accepted:-
1. Owing to in-flight vibrations and pulsating aerodynamics this crack may have propagated resulting in exhaust gases contacting the helicopter structure and thereby leading to a possible fire hazard.
2. Turbulent air flow so developed in the downstream of the tail pipe may result in upstream instability leading to an unstable operation of the engine.
That's how far I could see.
Any more possibilities, comments on the implications please.
Thanks for the read anyway.
Now the meat part.
There was a one inch crack detected at the end of this pipe during a turn around servicing (the welding had given away). The discussion was "How bad things would get if the helicopter was flown back to the repair depot with the known fault still existing". Though legally I agree that it cannot be a good decision, nevertheless following implications were considered, had the decision to fly back to repair depot was accepted:-
1. Owing to in-flight vibrations and pulsating aerodynamics this crack may have propagated resulting in exhaust gases contacting the helicopter structure and thereby leading to a possible fire hazard.
2. Turbulent air flow so developed in the downstream of the tail pipe may result in upstream instability leading to an unstable operation of the engine.
That's how far I could see.
Any more possibilities, comments on the implications please.
Thanks for the read anyway.
...or he might be referring to the exhaust extension on the Bell Medium twin (the part that the engine exhaust ejects into, which carries the exhaust gases to the exhaust deflectors). I think these connect to the airframe in 3 places and the mounts are known to crack, and they can be cracked for a long time before being detected. They usually get sent away for specialist welding repair. If it were detected in the field I wouldn't have an issue flying the helicopter back to a repair facility (if requested by maintenance), and once there ground the helicopter for repair.
I've also seen the sheet metal cracked in the place described by the OP, and from what I remember the crack was found to have been previously "drill stopped", however during susequent service the crack had migrated past the repair. So in this instance the decision had been made to keep flying, with the intention to change it at the next opportunity.
I've also seen the sheet metal cracked in the place described by the OP, and from what I remember the crack was found to have been previously "drill stopped", however during susequent service the crack had migrated past the repair. So in this instance the decision had been made to keep flying, with the intention to change it at the next opportunity.
Last edited by gulliBell; 21st Jan 2013 at 20:53.
If it is a 212 / 412 with the Alpine Exhaust Deflector STC the MM Supplement states the following
Repairs to the item(s) referenced within this document are not permitted. Contact Alpine Aerotech Ltd. for further information if repairs are required to the item(s) referenced within this document.
and
CAUTION: Do NOT operate the aircraft with only one Exhaust Deflector, Assy installed.
Repairs to the item(s) referenced within this document are not permitted. Contact Alpine Aerotech Ltd. for further information if repairs are required to the item(s) referenced within this document.
and
CAUTION: Do NOT operate the aircraft with only one Exhaust Deflector, Assy installed.
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Mmmm ...
gulliBell ...has pretty much summed it up .... if we assume its a 412 ... then 'stop drill' the crack ... fly the machine back to base TIG weld repair ...
At some stage of our careers we DO have to trust that our engineer brothers know what their doing ... lets try not second guess them!!
Legality should not be an issue if an appropriate entry is made in the 'tech log'.
gulliBell ...has pretty much summed it up .... if we assume its a 412 ... then 'stop drill' the crack ... fly the machine back to base TIG weld repair ...
At some stage of our careers we DO have to trust that our engineer brothers know what their doing ... lets try not second guess them!!
Legality should not be an issue if an appropriate entry is made in the 'tech log'.
Last edited by spinwing; 21st Jan 2013 at 23:14.
