In the beginning is the PATT meeting, somewhere in the UK ~2 months before the start of a new semester. At that time a great light shines upon the schedule, in that time allocations are set. And yet there is trouble on the face of the deep, and multitudes of constraints gather round. Problems of source availability rise up and are fearsome.

Time allocation is constrained only by number of shifts, but scheduling is affected by distribution in RA. It would seem that the only region of interest in the Galaxy is Orion/Taurus. The congestion for semester 94A was so severe that ITAC was asked to set priorities, and some observers were rather surprised to find their objects of interest accessible for only half the scheduled time. For other parts of the sky specific programmes can generally be placed within two weeks of the ideal time, although the offset can get pushed to a month. For some programmes, such as those with two sources twelve hours apart in RA, the very concept of 'ideal time' becomes a little fuzzy.

Constraints upon the schedule are numerous: Service time also has RA preferences; flexible scheduling requires programmes with compatible receiver requirements to be adjacent; minimising travel time and costs for observers requires other programmes be adjacent; E&C has very restricted times, with major engineering (now 'Eng') blocked in as dictated by the overall engineering programme at JAC and by the need to avoid conflicts with UKIRT which competes for the same engineers; suitable times for measurement of telescope and receivers (now 'C&C') is controlled by lunar phase for efficiencies, availability of suitable planets for beam maps, RA ranges for spectral line standards, and by a general need to be spread out in time; DDT requires a reasonable spread in time and RA; interferometry time is dictated by negotiations with CSO; UKT14 is unavailable for 5 days every 5 weeks at times that avoid weekend work with its attendant overtime; Rx C2 and B3i are each unavailable for 7 days every 2 months; Rx A2 is unavailable for 7 days every 3 months which is particularly troublesome because everybody wants A2. Final insult in the convoluted process of assembling a schedule is to have it all working perfectly except for a four-shift programme that must fit into a three-shift gap.

Another important set of constraints are the 'impossible dates' listed by observers, further complicated by the large time lag between proposal writing and schedule creation during which the lists change substantially. The custom has been to distribute a tentative schedule which provokes a flood of replies detailing previously unmentioned meetings, teaching requirements, time scheduled on other telescopes, conferences, holiday plans, etc, etc. Reworking the schedule on the basis of such replies is an iterative process that converges slowly with much anguish, wailing and gnashing of teeth. In future I intend to solicit, by e-mail, an updated list of 'impossible dates' before creating an initial schedule in an attempt to avoid the iteration process altogether. To aid in this, JCMT users are respectfully requested to provide a working Internet e-mail address on their proposal. An honest attempt will be made to avoid 'impossible dates' but it is not always possible.

Chris Purton, JAC