Contents lists available at ScienceDirect Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal Total air temperature anomalies as a metric for detecting high- altitude ice crystal events: Development of a failure indicator heuristic Álvaro Rodríguez-Sanz a, ⁎ , Rosa Arnaldo Valdés a , Fernando Gómez Comendador a , Eduardo Sánchez Ayra b , Javier Cano Cancela c,d a Universidad Politécnica de Madrid (UPM), Spain b Universidad Politécnica de Madrid (UPM), A330/A340 Captain at IBERIA Airlines, Spain c Universidad Rey Juan Carlos, Spain d The University of Auckland, New Zealand ARTICLEINFO Keywords: HAIC TAT anomalies Failure heuristic System reliability FDM ABSTRACT High-Altitude Ice Crystals (HAIC) constitute a hazard to commercial aircraft flying near deep convective weather due to jet-engine power loss and air data probes malfunction. HAIC can stick to warm metal surfaces in jet-engines and cause engine surge, stall, flameout and rollback, power loss, as well as engine compressor damage due to ice shedding. Along with these events, dis- ruption to aircraft systems are noted when HAIC are ingested into air data probes (Pitot tube and/ or Total Air Temperature -TAT- sensor), causing erroneous measurements of temperature and air speed. Particularly, the TAT probe incorrectly reporting zero degrees Celsius or in error is known to be evidence of ice crystals in the atmosphere surrounding the aircraft. These TAT anomalies are due to the accumulation of ice crystals in the TAT sensor, producing a zero degrees Celsius reading, generating failures in airspeed indicators and acting as potential incident/accident precursors. In this paper, TAT events from pilot reports and Flight Data Monitoring (FDM) are analyzed. TAT FDM data analysis covers two types of engines, which are used on short, medium and long- range routes. The study includes eight aircraft fleet types. Based on these analyses, we present a sensor-failure-tolerant heuristic that generates a re- liability indicator, founded on the differences between the TAT and the engine's inlet temperature sensors. It aims to provide early warnings to pilots regarding HAIC events and prevent potential data errors and system failures. 1. Introduction High-Altitude Ice Crystals (HAIC) represent a major weather hazard to commercial aviation flying in the vicinity of convective weather [1], mainly due to jet engine power loss and air data probes malfunction [2–4]. In the mid-90s, several commercial jet airplanes experienced frequent engines power-loss in ice particle conditions, which fostered research and awareness, resulting in the identification of similar events on other aircraft. Since then, the number of reported events has increased and they have sparked interest within the industry [5]. Therefore, the incidence of power-losses and other engine damages in commercial airplane jet https://doi.org/10.1016/j.engfailanal.2019.07.041 Received 25 November 2018; Received in revised form 6 June 2019; Accepted 15 July 2019 ⁎ Corresponding author. E-mail address: alvaro.rodriguez.sanz@upm.es (Á. Rodríguez-Sanz). Engineering Failure Analysis 105 (2019) 982–1005 Available online 18 July 2019 1350-6307/ © 2019 Elsevier Ltd. All rights reserved. T