Hi Skywatcher,

I'd be happy to answer these questions for you.

1. if weather is an issue, has the Tower said, weather is an issue, you must divert?

**Tower does not instruct a flight to divert. This is a common misconception.
Pilots are made aware of the most up to date weather and pilots will decide if they will commence an approach to land.
In virtually all cases, the flight crews tell controllers they are diverting and where they are diverting to.

2. do pilots decide if weather is an issue and cannot risk landing, so they ask to go to Pearson?

**Yes, Pilots will assess the latest weather as well as reports from other pilots who have tried the approach to land and make a determination of whether or not to try an approach.
Risk isn't really an issue as, no matter how bad conditions are, the flight crew can only fly so far into the approach and must abandon the landing IF they do not have the runway environment VISUALLY by a predetermined point. These limits are designed to keep them clear of ALL obstacles and provide a clear path of flight away from the airport in the event of an "overshoot".

3. who would decide and why, in particular, to circle around Peterborough? Would this be because Pearson was too busy to accept a Porter flight, so wait until we call you? Is this why it circled around land instead of circling around water? Or is that too dangerous to do?

**There are usually predetermined holding points for aircraft for each airport, however, the controller may select from many other available areas to hold a flights based on traffic and workload. I don't know the specifics for that evening but it is certainly possible that this flight was holding for a slot to open up at Pearson. There aren't restrictions or issues about holding over water. Certainly small single engined aircraft should remain within gliding distance of land in the event of engine problems, but this is not normally the case for larger, multi engine, commuter traffic.

4. We have noticed that if a Porter flight is very late it sometimes diverted to Hamilton. Why is that? Does Hamilton have no curfew?
** There is no curfew at Hamilton and it handles cargo flights throughout the night. Pearson only has a limited number of "overnight" slots and may not always approve a late arrival (rare but it does happen). Therefore, Hamilton is used in this instance.

Hope this helps.
Please advise if you need any clarification or further info.

Take Care!
Joe