Re: differents in DC10-30 and -40

Date:         27 Aug 97 03:57:53 
From:         stevec00@juno.com (Joel S Cole)
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	I found it interesting that you say some operators land DC10-30
with CLG retracted to save landing fee costs.  I know that you can land
with CLG retracted, but I thought there was a GW penalty or a special
inspection required in cases of an emergency landing.  There are some
potential consequence.  (I know there is a TOGW penalty.)

	Several parts of the Main L/G are Life Limited; with different
limits for different TOGWs.  Life Limits are the total landing cycles a
part can be flown based on fatigue tests.  Operating the DC10-30 with CLG
Retracted requires tracking these parts and additional parts to a new set
of Life Limits.  Granted, this difference is small and operators probably
do not track the cycles for CLG Stowed for one or two landing.
	Here are some examples:

   PART NO. & NAME	  L I F E   L I M I T S
		      CLG Extended  	CLG stowed
  ARG7312 MLG Piston    65,000    	63,800 total cyc.
  ARG7331 Torque Link	27,300		23,900
  ARG7558 Fwd Trun Bolt	  -0-		41,600
  ARG7322 Side Brace	53,000		41,520

Note the Center L/G is considered a redundant structure and is not
critical to landing loads.  Therefore there are no Life Limited parts in
Center L/G Assembly.

	You can see the effect on the Main L/G parts if the aircraft is
operated with CLG stowed.  One part, the Fwd Trunnion Bolt, does not
normally have a life limit but when CLG is stowed it is required to be
tracked.  Taking the worse case part, the Side Brace, if 100 landing
cycles are flown with CLG stowed, it is equivalent of accumulating 127
cycles flying with the CLG.

     100 cycles[CLG stowed] X (53,000)/(41520) =  127

Or stated another way;

     Ratio [100/41520] = Ratio [127/53000]

Bean counter would think of it in these terms:

   A $150,000-part expends $2.83 of its total life per landing vs $3.61
for CLG stowed(using the Brace's figures).  Then applying the 127/100
cycle conversion, this would equate to $4.58--a 60% increase in cost.(*)

	Now, concerning A/C Jacking to stow CLG.  The CLG can be
retracted with the A/C on the ground but the strut pressure MUST be bled
off.  If not, the Retract Actuator will pull the CLG up and internal
pressure will extend the Piston, causing damage to the Retract Actuator
and possibly the Lock Links.

	Conversely, to extend the CLG on the ground, it can be done by
deflating the shock strut, extending the gear until fully locked and
servicing the Strut.  But then the CLG strut service must be done with a
strut keeper installed.  If this GSE part is not available, then the next
best method is to jack the A/C and fully extend the CLG strut--taking you
back to where you started.

	I hope this info is helpful.  United and American were NOT even
tracking the Life Limited parts until a few years ago, so don't be
surprised if many are not aware of this requirement.

				STeve Cole~
				STeveC00@juno.com

  (*) I disclaim any errors in my cost analysis.

PS:  In my questionable cost analysis, I think I could be accused of
double jeopardy.  I applied a cycle "cost" and then multiplied it by
difference in part usage cost: probably should not have done both.
Realistically the cost factor would be about 10% or so.