>Try
>

>create table test (Latitude decimal(30,10), Longitude decimal (30,10))
>
>declare @CenterLat float=47.7795
>declare @CenterLon float=-65.7191
>declare @SearchDistance float=250
>
> select * from (select * from test T
> cross apply (select SIN(@CenterLat/57.2957795130823) * SIN(Latitude/57.2957795130823) + 
> COS(@CenterLat/57.2957795130823) * COS(Latitude/57.2957795130823) * 
> COS(Longitude/57.2957795130823 -@CenterLon/57.2957795130823) as Temp) Temp
>  where (latitude>=@CenterLat - @SearchDistance/111.0 and latitude<=@CenterLat + @SearchDistance/111.0) and
> (longitude>=@CenterLon - @SearchDistance/111.0 and longitude<=@CenterLon + @SearchDistance/111.0)) X
> where  3958.75586574 * ACOS(case when Temp > 1 then 1 when Temp < -1 then -1 else Temp end) <=@SearchDistance

This is good code. I also tested it against the main table with close to 2000 records and the related records were returned as is.

Thanks