Down Time

The down time statistics are based on individual fault reports. In Table 1 I give the general down time statistics for period 43.

A total of 144 fault reports were submitted, with an average time lost of 8 min per fault, for a total down time of 1.2% (1.3% on scheduled observing nights). Of these, 96 reported no time lost, 47 reported $<$ 2 hrs lost, and 1 reported 2 or more hrs lost.

This compares to a down time of 0.5% over all nights (0.6% on scheduled observing nights) in period 42, and 0.4% over all nights (0.4% on scheduled observing nights) in period 41. Of the 85 fault reports reported in period 42, 59 reported no time lost, 26 reported $<$ 2 hrs lost, and none reported 2 or more hrs lost. Of the 79 fault report in period 41, 57 reported no time lost, 22 reported $<$ 2 hrs lost, and none reported 2 or more hrs lost.

Table 1: Technical down time statistic period 43: 2011-04-01 to 2011-10-01

Night included	Time lost	Nights	Percentage$^a$	Last semester	Last Summer
All nights	1165 min	183	1.2%	0.5%	0.4%
Scheduled observing nights$^b$	1070 min	157.5	1.3%	0.6%	0.4%
Technical nights	95 min	22.5	0.8%	0.0%	0.7%
Service nights$^c$	400 min	50.5	1.5%	1.1%	0.1%
Visitor instruments	0 min	3	0.0%	0.0%	0.0%
$^a$ Taking the average length of time within nautical twilight. Exact numbers for each night
are used when looking at ``All nights''
$^b$ Excluding technical nights and visitor instruments
$^c$ Excluding service nights with SOFIN

The general conclusion is that there was a significant increase in the number of fault reports and the level of downtime. However, with reference to Table 2 and the Section ``Main problems'' this can largely be explained by the introduction of the new detector controller for the ALFOSC CCD plus some incidental errors. In particular, there does not seem to be any specific trend or any systematics in the frequency or the amount of time lost due to faults.