* Commercial, executive jet deliveries rise to 34 in Q1
* Delivers 21 regional jets, sells only 12 in the quarter
* Backlog slips to $14.7 bln, from $15.4 bln at end of 2011
By Brad Haynes
SAO PAULO, April 17 (Reuters) - Brazil's Embraer , the world's third-largest commercial aircraft maker, picked up the pace of first-quarter deliveries, but commercial jet sales lagged, raising questions about the stability of its future revenue.
Embraer delivered 34 commercial and executive jets in the quarter, up from 28 a year earlier, according to a securities filing. The company delivered 21 commercial planes but booked only 12 new orders in the segment, drawing down its backlog of firm orders to $14.7 billion, compared with $15.4 billion at the end of 2011.
Embraer has struggled to build up its backlog, representing potential revenue, after a downturn in the global aviation industry following the 2008 financial crisis.
The company forecast that stable demand this year in the regional aviation market will allow it to replace deliveries of its E-Jets with new orders of similar value.
But executives have said they do not expect a rebound in demand for private jets until 2013. Embraer delivered 13 private aircraft in the first quarter, compared with eight executive jets a year earlier.
The aircraft maker separately reports its defense unit's deliveries and backlog, which rose to an historic high of $3.4 billion last month.
Embraer's chief regional jet rival, Canada's Bombardier Inc , said last month it expects plane deliveries to dip in 2012 due to weak demand for its commercial jets.
Embraer shares edged up 0.3 percent in early Sao Paulo trading, while the benchmark Bovespa stock index rose 1.4 percent. The stock hit a four-year high last week after President Dilma Rousseff announced a new package of tax cuts and subsidized loans to boost Brazilian industry.