L-410 stalled as bid to return to airport failed

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Brazilian investigators have catalogued a series of problems which led a Let L-410 turboprop to stall and crash as its pilots tried to cope with engine failure after take-off.

Operated by Nordeste Aviacao Regional Linhas Aereas, the aircraft (PR-NOB) had departed Recife's runway 18 when, at a height of 20ft, its left-hand GE Aviation Czech M601E lost power.

Although the first officer suggested aborting the departure, the captain argued that there was not enough remaining runway to land the L-410.

Brazilian investigation authority CENIPA determined that the aircraft was 131kg heavier than the maximum take-off weight for the conditions, according to the manufacturer's operations data.

The inquiry found the increased weight - as well as the landing-gear, which was not immediately retracted - restricted its performance. But it states that, although a climb rate of 143ft/min should have been achievable, this "did not happen".

It points out that rudder deflection is needed to maintain the attitude necessary to counter the yaw of asymmetric flight.

After crossing the coast, at a height of 400ft the crew began a right turn with the intention of returning to the airport, rather than continuing the engine-failure procedure which instructed acceleration and a climb to 1,500ft. The inquiry suggests that truncated training exercises might have contributed to this decision not to climb to a "more comfortable" height to begin a single-engined approach.

CENIPA says the aircraft's pitch increased, resulting in its airspeed bleeding away, while its bank angle reached up to 20°, exceeding recommended limits.

Just over 2min after take-off the captain abandoned the right turn - possibly realising the aircraft could not intercept the runway 36 approach - and turned left instead, against the practice of avoiding banking to the side of the failed engine. The left-hand engine is also the L-410's critical powerplant.

The crew allowed an "excessive" sideslip of around 20° to develop, sapping the aircraft's airspeed and height, says the inquiry.

Sink-rate warnings alerted the pilots to the loss of altitude, while the airspeed dropped below the 84kt minimum-control threshold.

CENIPA indicates friction in the L-410's cockpit, indicating an "excess of confidence" from the captain and contrasting this with the first officer's apparent awareness of the aircraft's predicament - pointing out that he "repeatedly" tried to convince the captain to attempt an emergency landing on the beach.

Investigators determined that the aircraft's stall speed was around 75kt. Although a stall warning sounded continuously for 19s, says the inquiry, there is "no evidence" that the aircraft changed its trajectory before it stalled, rapidly rolling to the left and hitting the ground. Neither pilot, nor any of the 14 passengers survived the 13 July 2011 crash.