The War Diaries of the 15th Scottish Div are on-line here:
https://www.15thscottishdivisionward...uk/war-diaries
There is a "Search All" button in the lower right which strings all the individual diaries together and allows searching in all diaries at once. I tried several terms but came up with nothing, maybe someone else will have better luck. You can even use the "Search All" to jump to the September entries for each of the units and quickly check activity on the 18th. (Use the phrase: Month and Year Sep) I found nothing about a shoot down.