Suramericanas B722 at Bogota on May 6th 2015, engine failure distributes debris over city
Last Update: October 27, 2016 / 17:00:01 GMT/Zulu time
Colombia's GRIAA have opened an investigation into the occurrence rated a serious incident.
Colombia's DGCA reported an engine of the cargo flight failed causing debris to affect the area of Fontibon, located just south of the aerodrome at about the crosswind leg of runways 13, at about 07:15L (12:15Z).
Colombia's GRIAA reported in a first preliminary statement, that the aircraft was climbing out of Bogota's runway 13R when immediately after selecting the gear up a blow was felt to the aircraft, the EGT readings of engine #1 (left hand engin) became abnormal prompting the crew to reduce thrust on that engine. The crew advised ATC of the engine failure and requested an immediate return to the airport, the aircraft landed safely back on runway 13L 14 minutes after departure, the crew advised no further assistance was needed and taxied the aircraft to the apron. Residents around the airport collected debris of turbine blades, that had been distributed into the neighbourhood. A visual inspection revealed fractures of turbine blades at the rear section of the engine.
In October 2016 the GRIAA released their final report in Spanish concluding the probable causes of the serious incident were:
- internal ducts 3,4,5 and 10 cooling the rotor blade #1 of the first stage of the high pressure turbine were blocked by contamination with silicon, probably because of ingestion of sand.
- fracture of the rotor blade #1 of the first stage of the high pressure turbine due to stress and fatigue in areas presumably affected by intergranular corrosion
- A borescopic inspection of the #1 engine, required to be conducted every 600 engine operating hours according to chapter 8 of the engine maintenance manual, was not completed.
The GRIAA reported that just when the flight crew, consisting of captain (63, ATPL, 14,655 hours total, 8,449 hours on type) and a first officer (26, CPL, 1,709 hours total, 1,481 hours on type), selected the gear lever up, a loud bang was heard, the crew noticed engine #1 was showing abnormal EGT indications, reduced power on the engine and initiated a return to Bogota for a landing on runway 13L without further incident.
A visual inspection of the left hand engine showed blade damage to the first stage of the high pressure turbine, the airframe suffered no damage. Residents about 1170 meters/3840 feet past the runway end found blade debris distributed over an area of about 270 meters length and 115 meters width.
Further inspection revealed blade #21 of the first stage of HPT showed thermal damage, the blade #1 had fractured about 2.1 to 2.4 inches above the blade root. The blade #1 cooling holes 3,4,5 and 10 were completely blocked, a number of other blades also showed obstruction of up to two cooling holes. Lab analysis by the engine manufacturer identified the blockages consisted of enriched silicon typical for sand ingestion. The #1 blade showed a crack from the #4 cooling hole towards the edge of the blade, the crack surface looked very old, the crack was mainly caused by fatigue. The actual fracture was caused by tension. A metallurgic examination of the crack and fracture revealed intense oxidation near the cooling hole consistent with intergranular corrosion (rust) causing impoverishment of the blade's alloy.
The GRIAA analysed that there had been no maintenance records between the years of 2000 and 2007 disabling the investigation to verify any maintenance done and operating hours during that time. Maintenance records resumed in 2007. The last borescopic inspection of the #1 engine had been done on Aug 14th 2013, the engine had since operated 839 hours. Therefore it is clear that the required borescopic inspection after a maximum of 600 operating hours had not been conducted.
This article is published under license from Avherald.com. © of text by Avherald.com.
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