* Q2 revenue falls for 9th straight quarter
* Q2 revenue in trucks business falls 5.5 pct
* Reaffirms 2017 revenue, adj EBITDA forecast (Adds details from conference call, analyst comment and updates shares)
June 7 (Reuters) - Navistar International Corp posted a quarterly loss, compared with a year-ago profit, partly due to a $60 million charge related to used-truck inventories and said it expected overall market conditions to improve in the second half.
The truck and engine maker's shares were down 1.5 percent at $29.47 on Wednesday.
Revenue in Navistar's truck business, its biggest, fell 5.5 percent to $1.40 billion in the second quarter ended April 30.
The results come in the backdrop of improving heavy truck orders. The orders had been declining as trucking companies adjusted their fleets amid lackluster retail sales and industrial output in the United States.
Orders for Class 8 highway trucks in the United States, the 18-wheelers that haul freight across the country, soared 77 percent in April versus the same period a year earlier, according to preliminary data from industry forecaster FTR. (http://bit.ly/2r239kc)
"At this point in time, we are confident we can deliver year-over-year improvement," Chief Executive Troy Clarke said.
Navistar reaffirmed its revenue and adjusted earnings before interest, tax, depreciation and amortization (EBITDA) forecast for the year and said it expected a stronger second half as its turnaround efforts start to pay off.
The Lisle, Illinois-based company, which was once a leading maker of truck engines, is in the process of turning itself around after making a disastrous bet on a costly and unsuccessful proprietary smog-reduction system that did not meet regulatory standards.
The company, which also makes school buses and dump trucks, has changed management, cut costs and redesigned its products, in a move to return to profitability.
"Guidance calls for improved EBITDA in 2017 and a significantly stronger second half to the fiscal year on sequential improvements in the company's core markets," Jefferies analyst Stephen Volkmann said.
Navistar said the $60 million charge was a result of a change in its sales strategy for its used MaxxForce 13 trucks to focus more on export sales.
Net inventory on April 30 was $1.46 billion compared with $1.55 billion at the end of April last year.
Net loss attributable to the company was $80 million, or 86 cents per share, in the quarter, compared with a profit of $4 million, or 5 cents per share, a year earlier. (http://bit.ly/2sS8OuI)
Revenue fell 4.6 percent to $2.10 billion. The company reported a fall in revenue for the ninth straight quarter.
Up to Tuesday's close, Navistar's shares had fallen 4.6 percent this year. (Reporting by Arunima Banerjee in Bengaluru; Editing by Shounak Dasgupta)