* Sales rise 0.4 pct in Sept. on aerospace, primary metals
* Excluding aerospace, sales fell 0.7 pct
* Gains in eight of 21 industries
OTTAWA, Nov 15 (Reuters) - Canadian manufacturing sales grew 0.4 percent in September from August due mainly to a sharp rise in the volatile aerospace sector, with sales falling in the heavyweight auto industry and in most other industries, Statistics Canada said on Thursday.
Analysts surveyed by Reuters had forecast, on average, a 0.3 percent gain in factory sales in the month.
Sales rose in just eight of the 21 industries surveyed. Excluding the aerospace product and parts industry, manufacturing sales fell 0.7 percent.
In volume terms, overall sales were up 0.4 percent.
Production in the aerospace product and parts industry surged 43 percent - the biggest jump since May. Figures for this sector tend to have a disproportionate influence on overall manufacturing data because of the magnitude of the orders and lengthy production period.
Strength in September also came from the primary metals industry, where sales rose 3.7 percent due in part to higher prices. Auto sales, which have made a big comeback so far this year, fell 3.6 percent in September.
New orders for factory goods rose 2.2 percent while unfilled orders slipped 0.3 percent.
Manufacturers continued to build inventories, which edged up 0.2 percent. The inventory-to-sales ratio was unchanged at 1.31 in September.