* Profit down 19 pct from year ago on weak deliveries
* Shares fall 4 pct to six-month intraday low
SAO PAULO, Oct 31 (Reuters) - Brazil's Embraer SA posted an unexpected drop in quarterly profit on Thursday due to delayed aircraft deliveries, but the world's third-largest commercial planemaker stood by its 2013 forecasts on hopes for a strong fourth quarter.
Third-quarter net income fell 19 percent from a year earlier to $52.9 million, according to a securities filing, missing analysts' average estimate of $75 million in a Reuters survey.
Embraer delivered 58 planes to airlines in the first nine months of the year, less than two-thirds of its full-year forecast of 90 to 95.
"Our third-quarter numbers were a little below what we expected because of some delayed deliveries," Chief Financial Officer Jose Antonio Filippo said on a call with reporters. "We still confirm our annual delivery guidance - obviously, at the bottom end of that range."
Embraer shares fell more than 4 percent in Sao Paulo to a six-month low as the weak results underscored questions about this year's profitability targets.
Earnings before interest, taxes, depreciation and amortization, a gauge of operating profit known as EBITDA, fell 7 percent to $156.4 million, missing analysts' average estimate of $172 million.
EBITDA as a share of net revenue, a measure of profitability known as the EBITDA margin, came to 12.1 percent, little changed from a year earlier, when the restructuring of a customer's financing weighed on results.
Embraer's 11.7 percent EBITDA margin in the first nine months of the year is far short of its target of 13 percent to 14 percent for 2013.
The EBIT margin, another profitability gauge that includes depreciation and amortization, was 6.4 percent through September, well below the 9 percent to 9.5 percent target.
Filippo said the company still expects to meet its EBIT and EBITDA targets on the basis of a strong fourth quarter.
Embraer initially reported earnings in Brazilian reais, using accounting standards that showed a 10 percent drop in net income from a year earlier.