ASN Wikibase Occurrence # 317462
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| Date: | Friday 26 July 2013 |
| Time: | 21:42 UTC |
| Type: |  ATR 72-500 (72-212A) |
| Owner/operator: | Trip Linhas Aéreas |
| Registration: | PP-PTU |
| MSN: | 891 |
| Year of manufacture: | 2010 |
| Fatalities: | Fatalities: 0 / Occupants: 62 |
| Aircraft damage: | None |
| Category: | Serious incident |
| Location: | Esplanada, BA -
 Brazil
|
| Phase: | En route |
| Nature: | Passenger - Scheduled |
| Departure airport: | Maceió-Zumbi dos Palmares Airport, AL (MCZ/SBMO) |
| Salvador-Deputado Luís Eduardo Magalhães International Airport, BA (SSA/SBSV) | |
| Investigating agency: | CENIPA |
| Confidence Rating: |  Accident investigation report completed and information captured |
Around 2142 UTC, on FL160, the aircraft entered a region that had the conditions of ice accretion. Although the aircraft anti-icing was activated, the air pneumatic de-icing was not activated by the flight crew. Then, there was a significant degradation of aircraft performance, leading to a reduction in the Indicated Airspeed (IAS).
The aircraft initial cruise speed was 202kt. The aircraft lost 10 kt prior to the activation of anti-icing. The crew heard a noise described as similar to that of a compressor stall, followed by a loud vibration.
The aircraft reached 180 kt when the power levers were reduced to 20% TQ, leading the IAS to reduce down to 148 kt, and the autopilot was disconnected. The crew did not identify the cause of the vibration.
Approximately 4 second after the autopilot was disconnected, the Angle of Attack (AOA) increased, resulting in the activation of the stall protection systems (stick shaker and stick pusher). The pilots counteracted the pusher, which resulted in the loss of aircraft control. During the loss of control, Pitch Uncouping Mechanism (PUM) triggered.
The crew declared emergency and, upon reaching the FL110, the control of the aircraft was restored. Landing was performed in a controlled way at the destination Salvador International Airport, BA (SSA).
The aircraft was not damaged. The 4 crewmembers and 58 passengers left unharmed.
Contributing factors.
- Control skills – a contributor.
The reduction in power in both engines, associated with the attempt to maintain level flight resulted in the decrease of the IAS to values below the minimum operating speed under the conditions encountered; increased angle of attack; and the subsequent activation of stall protection systems.
- Adverse meteorological conditions – a contributor.
The weather conditions observed on the level and route of the PP-PTU, without the aircraft having the de-ice system activated, caused ice accumulation and a significant loss of airspeed. This condition, aggravated by inadequate actuation in flight controls, led the aircraft to a stall condition.
- Crew Resource Management – a contributor.
It was found that there was inefficiency in the use of available human resources for aircraft operation, due to inadequate management of tasks affecting each crewmember because of the confusion in communication, given the misinterpretation regarding the need for engine shutdown during the occurrence.
- Piloting judgment – a contributor.
There was an inadequate assessment by the crew of the parameters related to the operation of the aircraft, regarding the non-activation of the de-icing system for the presented ice formation conditions, as well as regarding the use of flight commands when trying to counteract the stick pusher performance in a stall situation.
- Aircraft maintenance – undetermined.
The absence of the Red Bug from the left-hand speedometer, which was not recorded in the technical logbook, indicated that, at the time of the serious incident, there was no perception by crews and maintenance crews about the importance of observing the minimum operating limits at icing conditions, which may have contributed to this speed limit not being respected in this operation.
- Perception – a contributor.
During the flight, there was an inaccurate perception of the impact of ice accretion conditions on the air operation, which favored the crew to keep the flight in unfavorable conditions and not realize the occurrence of stall caused by ice accumulation.
- Decision-making process – a contributor.
There was an inadequate assessment of the factors that impacted in the aircraft performance, which undermined the recognition of the severe icing condition and resulted in the adoption of wrong measures to manage that adverse situation.
Accident investigation:
 |
|
Sources:
IG-136/CENIPA/2013
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 14-Jul-2023 19:54 | harro | Updated |
Corrections or additions? ... Edit this accident description
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