select distinct [date], [flight number],
dcount("1","tableName","[flight number]='" & [flight number] & "' and successful=-1)/dcount("1",""tableName","[flight number]='" & [flight number] & "'")*100 as PercentSuccess,
dcount("1","tableName","[flight number]='" & [flight number] & "' and successful=0)/dcount("1",""tableName","[flight number]='" & [flight number] & "'")*100 as PercentFailure from tableName;
Yes: IIf([Successful]="Yes","1","0")
Yes: IIF([Successful] = True, 1, 0)