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Topic: CRJ Family & ERJ Family Service Life
Posted 2012-12-30 10:42:54 and read 4739 times.

I performed a quick Airliners.net Tech/Ops forum search for the Service Life or Service Objective of both the CRJ Family (100, 200, 700, and 900) and the ERJ Family (135, 140, and 145) but could not find such information.

Therefore I am asking if any current member of the forum knows the number of cycles at which any member of the CRJ or ERJ Families reaches their Service Life/Service Objective? I understand that Service Life and/or Service Objective are dependent on fatigue spectrum (maneuvering, stage length, etc) therefore I am only looking for "typical" values.

My curiosity stems from a recent flight on an ERJ145. While boarding I noticed a main entry door corner doubler repair, typically an indicator of fatigue damage. I performed quick mental math and realized the Service Life and/or Service Objective of a regional jet must be relatively high.

(These numbers are assumptions to prove a point)
If the "typical" flight time of a regional jet is 1.5 hours and the "typical" turn around time is 0.5 hours we can say the "typical" arrival-departure time is 2.0 hours. Assuming the airplane starts service at 600 and ends service at 2200 each day for six days a week (leaving one day for maintenance or scheduling), the plane builds approximately 8 cycles per day or 48 cycles per week or roughly 2,500 cycles per year.

Early build CRJ200 and ERJ145 airplanes were delivered in 1998, meaning those airplanes "may" have (over approximately 14 years) 35,000 cycles. That is not an absurdly high number of cycles but it is "getting up there."

Anyway, does anyone know the number of cycles at which any member of the CRJ or ERJ Families reaches their Service Life/Service Objective?

Topic: RE: CRJ Family & ERJ Family Service Life
Posted 2012-12-30 22:01:54 and read 4599 times.

 Quoting amccann (Thread starter):My curiosity stems from a recent flight on an ERJ145. While boarding I noticed a main entry door corner doubler repair, typically an indicator of fatigue damage.

A door corner doubler is almost always due to impact damage, but that's a different issue. The ERJ145, like all modern airlines, is a damage tolerant design. As a result, it's expected to develop fatigue cracks prior to its design service life. The entire point of damage tolerant designs is to assume that undetectable cracks are present at day one and then inspect for and catch them before they reach critical length. If a modern jet reaches it's design service life without any cracks then it was either incredibly lucky or grossly over-designed.

Tom.

Topic: RE: CRJ Family & ERJ Family Service Life
Posted 2012-12-30 22:50:44 and read 4580 times.

 Quoting tdscanuck (Reply 1):As a result, it's expected to develop fatigue cracks prior to its design service life. The entire point of damage tolerant designs is to assume that undetectable cracks are present at day one and then inspect for and catch them before they reach critical length. If a modern jet reaches it's design service life without any cracks then it was either incredibly lucky or grossly over-designed.

This conversation furthers my interest in the Service Life/Service Objective of the CRJ or ERJ Families. Now that I think of it the doubler repair in question is one of only few doubler repairs I have seen on a CRJ or ERJ airplane. (However I have only lately, within the past few months, been looking for doubler repairs on CRJ or ERJ airplanes.) It seems logical with the increasing regional jet cycles and damage tolerance principles that doubler repairs would/will be more common as regional jet cycles continue to increase.

Topic: RE: CRJ Family & ERJ Family Service Life
Posted 2012-12-31 00:03:31 and read 4558 times.

 Quoting amccann (Reply 2):It seems logical with the increasing regional jet cycles and damage tolerance principles that doubler repairs would/will be more common as regional jet cycles continue to increase.

Sure. However remember that airliners are designed and built for the expected type of operation. For RJs, you're talking multiple daily cycles. For a 777, you're talking one daily cycle. So it doesn't follow that RJs necessarily fall apart earlier if you compare cycle for cycle.

Topic: RE: CRJ Family & ERJ Family Service Life
Posted 2012-12-31 15:36:48 and read 4403 times.

 Quoting Starlionblue (Reply 3):Sure. However remember that airliners are designed and built for the expected type of operation. For RJs, you're talking multiple daily cycles. For a 777, you're talking one daily cycle. So it doesn't follow that RJs necessarily fall apart earlier if you compare cycle for cycle.

Correct, for that reason the fatigue spectrum is important. However a basic SN curve will demonstrate the "primary" driver of fatigue is cyclical loading. It is reasonable to state that a properly designed long haul product at X number of cycles will have the same probability of cracking as a properly designed short haul product at X number of cycles if their Service Life is similar.

Topic: RE: CRJ Family & ERJ Family Service Life
Posted 2012-12-31 16:16:15 and read 4391 times.

 Quoting amccann (Reply 4):It is reasonable to state that a properly designed long haul product at X number of cycles will have the same probability of cracking as a properly designed short haul product at X number of cycles if their Service Life is similar.

The *probability* is the same; 1 in both cases. However, at the same number of cycles a short haul aircraft should have much *smaller* cracks because it was built to a higher service life. In order to have economical maintenance intervals, short haul aircraft with higher cycle designs have to run at lower stress.

 Quoting amccann (Reply 4):However a basic SN curve will demonstrate the "primary" driver of fatigue is cyclical loading.

The *stress* is hugely important (that's why it's usually log-log). An aircraft designed for a lot of cycles will tend to run at lower stress so that the cracks don't grow as fast.

Tom.

Topic: RE: CRJ Family & ERJ Family Service Life
Posted 2012-12-31 16:45:29 and read 4382 times.

The CRJ is designed for 60,000 cycles. I haven't seen the embraer MPD to see their numbers. See below for most airplanes.

http://www.gpo.gov/fdsys/pkg/FR-2010-11-15/html/2010-28363.htm

The 737 is designed for the most cycles of any airplanes in production at 75000 cycles which is higher than the CRJ at 60000 or A320 at 48000.

It is worth noting that all maintenance programs can exceed these numbers but they were the initial projected lifespans for the purpose of certification.

Topic: RE: CRJ Family & ERJ Family Service Life
Posted 2012-12-31 17:51:52 and read 4362 times.

Hi Roseflyer,

I remember reading that the CRJ was designed for an "economical" life of 60,000 hours I thought, although it could have been cycles. I also thought I remember reading that the Dash 8-100 had been extended to 120,000 cycles. Please correct me if I'm wrong.

Happy New Year everyone!

[Edited 2012-12-31 17:52:44]

Topic: RE: CRJ Family & ERJ Family Service Life
Posted 2012-12-31 18:24:51 and read 4344 times.

It would not surprise me if 1 cycle = 1 flight hour for the initial certification and when the maintenance program was established. However every airline is different. The a320 was 1.25 hours per cycle and 737ng 1.4 hours per cycle even though both are close to 2 hours per cycle.

Basically all airplanes have had their maintenance program extended beyond the initial life. Airbus is working on getting the A320 to 90000 cycles even though it was initially at 48000 cycles and then extended to 60000.

Topic: RE: CRJ Family & ERJ Family Service Life
Posted 2012-12-31 20:06:04 and read 4317 times.

 Quoting tdscanuck (Reply 5): The *stress* is hugely important (that's why it's usually log-log). An aircraft designed for a lot of cycles will tend to run at lower stress so that the cracks don't grow as fast.

Indeed. I was operating under the assumption that most commercial airplanes operate at "similar" levels of fatigue stress. However it makes a lot of sense that high cycle airplanes would operate at reduced fatigue stress. It is relatively obvious that a reduced fatigue stress results in an increased fatigue life, guess I should have stepped back and looked at the big picture. Heh.

 Quoting Roseflyer (Reply 6):The CRJ is designed for 60,000 cycles. I haven't seen the embraer MPD to see their numbers. See below for most airplanes. http://www.gpo.gov/fdsys/pkg/FR-2010...3.htm

Making some progress. Thank you!

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