Down Time

The down time statistics are based on individual fault reports. In Table 1 I give the general down time statistics for period 45.

A total of 86 fault reports were submitted, with an average time lost of 3 min per fault, for a total down time of 0.3% (0.3% on scheduled observing nights). Of these, 69 reported no time lost, 17 reported $<$ 2 hrs lost, and none reported 2 or more hrs lost.

This compares to a down time of 0.9% over all nights (1.1% on scheduled observing nights) in period 44, and 1.2% over all nights (1.3% on scheduled observing nights) in period 43. Of the 130 fault report in period 44, 95 reported no time lost, 33 reported $<$ 2 hrs lost, and 2 reported 2 or more hrs lost. Of the 144 fault reports reported in period 43, 96 reported no time lost, 47 reported $<$ 2 hrs lost, and one reported 2 or more hrs lost.

Table 1: Technical down time statistic period 45: 2012-04-01 to 2012-10-01

Night included	Time lost	Nights	Percentage$^a$	Last semester	Last Summer
All nights	287 min	183	0.3%	0.9%	1.2%
Scheduled observing nights$^b$	247 min	153.5	0.3%	1.1%	1.3%
Technical nights	40 min	21	0.4%	0.3%	0.8%
Service nights$^c$	197 min	54	0.7%	1.7%	1.5%
Visitor instruments	0 min	9.5	0.0%	0.3%	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

Both the numbers of fault reports and the total time lost in the semester are at an all time low, and no fault occurred that lost a large amount of time. Compared to the previous semesters this is, beyond the lack of any major problem, mostly due to the teething problems with the new detector controller for the ALFOSC CCD being under control.

In general, one can expect variations from semester to semester which can be due to a significant change such as the new CCD controller or a single major problem (which is bound to occur at some point), or simply because the weather is very bad so the telescope is used little (though this was not the case in the past summer semester). We keep track of the fault reports in a data-base system since October 2006 so we can give a more general indication of the long-term reliability of the telescope. Over the full 6 year period the total downtime over all nights has been 0.76%, varying on a yearly basis between 0.43% and 1.28%