Document ID: chunk:federal_register_of_legislation:F2009L03768:body:0:p2
Version: federal_register_of_legislation:F2009L03768
Segment Type: other
Provision Reference: 
Character Range: 3046–6185

by providing the flight crew with measurable and objective evidence and timely alert when such severe ice conditions are encountered.
             The accumulated experience on the worldwide fleet of commuter aeroplanes together with recently reported ATR42/72 in-flight incidents, show that a long exposure to severe icing conditions, outside the certification envelope, can result in "unsafe conditions".  This could lead to rapid performance degradation resulting in sudden stall of the lifting/controlling aerodynamic surfaces and subsequent loss of control of the aeroplane.
             Prolonged exposures to these severe icing conditions are due to the lack of crew awareness of these extreme environmental conditions leading to their late detection and/or untimely or incorrect application of the existing AFM procedures, which require the flight crew to actively monitor the encountered icing conditions and to leave them as soon as they are recognised as severe.
             Current ATR42 AFM emergency procedures for the encounter of severe icing conditions remain valid and must be applied by the flight crew.  However, their application is based on the detection of such severe icing conditions by means of flight crew subjective interpretation of:

                    * an unexpected decrease of the aeroplane speed and/or rate of climb and/or;

                    * a set of very different visual cues like ice covering unheated portion of either forward side windows, possibly associated with water splashing and streaming on the windshield and/or;

                    * several secondary indications based on visual observation of ice accretion on different parts of the airframe.
             All these together require the flight crew to perform a final qualitative judgement based upon its experience to fly icing conditions, and which could be different depending on the specific circumstances of each case where other concurrent environmental factors like poor light conditions, night operations, etc., can impair the decision-making process.

   In addition, even if the severe icing conditions are quickly identified by the crew and the escape manoeuvre promptly initiated, it may still take a few minutes for the aircraft to exit these conditions.
   In order to improve flight crew situation awareness in icing conditions, ATR developed a new function called Aircraft Performance Monitoring (APM) that is available on ATR aeroplanes with Multi Purpose Computer (MPC) installed.
   The APM processes a collection of different parameters (among them the aeroplane take-off weight as selected by the crew on a specific rotary selector), and in particular computes and compares the actual drag on the current flying path with the theoretical/expected value.  From the comparison, a measurable and objective determination of the performance degradation possibly due to abnormal ice accretion can be calculated.  When the performance degradation passes given thresholds, the APM annunciates warning signals by triggering up to two different levels of alerts while on climb/descent and three levels of alerts