COMMANDER TIPS: Prepare Properly for Flying In Icing Conditions

For those of us living in the northern hemisphere, it’s time once again to review system knowledge and procedures as they relate to anti- and deicing equipment before we embark on the next flight in IMC.

Equally important is to brush up on the nature and characteristics of icing as well as reacquainting ourselves with the regulatory aspects of flying in icing conditions. For example: Is the airplane certified for flying in known icing? What constitutes known icing? What equipment must be working before entering known icing conditions?

The following are some additional tips regarding the TPE331 when operating in icing conditions. For any issues regarding airframe icing and the effects of snow, ice, and cold air temperatures, etc. that have not been addressed in this article, please refer to your Aviation Weather Handbook and the appropriate Aircraft Flight Manual (AFM) for a more complete description of operating in icing conditions.

First, a few words to the wise:

Avoidance is the best method of coping with ice.

Certification for flight into icing conditions only ensures that the airplane is capable of safe flight through a limited range of icing conditions.

Prolonged operations in icing conditions should always be avoided, regardless of severity/type of icing and/or available anti-/deicing equipment.

Severe icing (e.g. freezing drizzle or rain) is considered outside of the FAA certification requirements.

Procedures and limitations published in the specific AFM or Pilot Operating Handbook (POH) take precedence over tips suggested in this article.

Now let’s discuss a few TPE engine operational topics with regards to icing conditions.

PREFLIGHT INSPECTION

• INLET: Remove the inlet covers and inspect the inlet for accumulation of ice or snow.
• T2 SENSOR: (Bendix Fuel Control) Inspect the inlet sensor for condition, security, and freedom from ice or snow accumulation.
• P2T2 SENSOR: (Woodward Fuel Control Unit) Inspect the inlet sensor for condition, security, and freedom from ice or snow accumulation. Pay close attention to the P2 sensor inlet hole and the anti-ice air (P3 air) discharge hole at the tip of the P2 sensor. Both should be unobstructed.
• PROPELLER: Carefully turn the propeller through (I suggest 10 to 20 blades) to reduce as much as possible the drag imposed by cold and therefore congealed oil.

NOTE: An incident occurred several years ago in a northern U.S. area, in which a preflight inspection revealed that ice had formed in both engine inlets. The crew decided to turn the propellers through by hand until the impellers could be freed.

Although unusual resistance was met, the propellers were pulled by force until the impellers broke free. After start, engine whine was so loud that the tower called, asking if there was a problem. The engines were shut down, and a visual inspection determined that both impellers were bent to the extent that both engines had to be disassembled and the impellers replaced.

• TAILPIPE: Remove the protective cover and inspect for ice or snow accumulations.

ENGINE START

• BATTERIES: Pre-heating the aircraft batteries under cold-soaked conditions will improve their performance. Removing and storing the batteries in a warm place overnight also will make a difference in starting capacities.

NOTE: Removing and re-installing batteries may constitute a maintenance action and could, therefore, require an entry in the logbook and a sign off by a certificated and/or licensed mechanic.

Noting indicated battery voltage at start initiation can provide an excellent early indication of potential starting performance problems. An excessive droop in indicated voltage (typically accompanied by very slow engine acceleration) means a suitably rated ground power unit should be used.

• FUEL ENRICHMENT: The use of fuel enrichment during a very cold engine start should be a little different than under starts initiated at warmer ambient conditions. Obviously, more attention to engine acceleration, especially in the 18 to 28 percent RPM range, is necessary. For those engines equipped with the Auto-Start feature, observe that the start sequence and rate of RPM rise progresses normally within the specified EGT/ITT limits. During manual starts, use fuel enrichment as necessary to maintain engine acceleration; once again, remain within the specified EGT/ITT start limits. Remember to observe any attendant fuel enrichment RPM range restrictions as noted in the AFM.

TAXI

• OIL PRESSURE: Oil pressure transients above normal limits are possible in cold ambient temperatures. Limit engine RPM as much as possible, to minimum idle speeds until oil temperature approach normal. When taxiing aircraft with cold oil, keep control inputs smooth and slow, and when possible, keep RPM changes to a minimum. Propeller response in Beta mode may be sluggish. Do not select high RPM or high power until the oil temperature is in the normal range.
• INLET HEAT: If flight in icing conditions is anticipated, test the engine anti-ice and in-flight ignition systems prior to departure. Selection of inlet heat at a stable power setting on the ground will normally produce a noticeable increase in indicated turbine temperature. Turbine temperature rise is due to the diversion of some air from the compressor section.

NOTE: During Inlet Heat ground checks, failure of the EGT (ITT) to rise could mean that the anti-ice valve did not open, or it could mean that the valve had been stuck in the open position prior to selecting engine anti-ice to ON. Therefore, if the proper operation of the engine anti-ice valve cannot be verified, flights into potential or known icing conditions must be delayed until the discrepancy has been corrected. See Honeywell Operating Information OI331-15, dated April 30, 1997.

TAKEOFF, CLIMB, CRUISE, APPROACH, LANDING

• PROPELLER GOVERNING: Propeller governing RPM is affected by oil temperature. With colder oil, governing RPM may be higher.
• IGNITION LH & RH to CONT (Continuous Ignition) should be used:
  • For all takeoff and landings with standing water/slush/snow
  • Before applying inlet heat if ice has accumulated
  • At any time ice has been observed shedding, until shedding has concluded.
  • At any time ice is suspected or observed to be collecting on the propeller spinners, wing leading edges or unheated propeller blade areas.
  • On final approach during or following operations in icing conditions
• IGNITION: In-flight ignition use and related cautions are addressed in the Honeywell Operating Information Letter OI331-11 R7, dated September 18, 2009.

NOTE: LACK OF RESPONSE TO THE POWER LEVER. The cause may be ice blockage of the P2 inlet sensor probe and can occur even when visible moisture is not present. If lack of response is observed, it is recommended that ignition and engine anti-ice be turned ON for both engines. This will introduce anti-icing air to the sensors (as well as the engine inlet) and normal response should return within approximately 3 minutes. Refer to OI331-13, dated April 27, 1995.

• ENGINE INLET ANTI-ICE (Inlet heat) should be used during all takeoffs, flights, and landings in actual and potential icing conditions.

If the use of engine anti-ice is delayed inadvertently until after encountering icing conditions, it must be assumed that ice has accumulated in the engine inlet throat area. In such instances subsequent application of engine anti-ice heat can cause ice shedding and ice ingestion, which may cause a brief airflow interruption through the engine and could result in an engine flameout. Therefore, if ice has formed, the first action prior to de-icing is to manually select continuous ignition [IGNITION LH & RH to CONT] for both engines. Then switch the engine inlet heat [ANTI-ICE > ENG INTAKE L & R] one engine at a time to reduce the risk of a double flameout.

Reportedly, several flameouts have occurred following descent out of icing conditions into warmer air. Remember also, that under some conditions, ice accumulation can be difficult to detect visually.

For more information on the proper use of engine inlet anti-icing and the engine ignition systems (duty cycle limitations, etc.) please review the Honeywell Operating Information Letter OI331-11R7, September 18, 2009

POSTFLIGHT

• SECURE: Install inlet and tailpipe protective covers before moisture can accumulate in these areas. If allowed, moisture may freeze and can effectively lock up the rotating group.

In conclusion, the above tips are intended to be supplemental to the published operating procedures. For a complete study on aircraft operations in cold and in icing conditions, refer to the FAA/CAA approved procedures and recommendations in the appropriate PILOTS OPERATING MANUAL, SYSTEMS DESCRIPTION, COLD WEATHER OPERATION and NORMAL PROCEDURES. You can also visit a free online course at: https://aircrafticing.grc.nasa.gov/.

Helmuth Eggeling previously served as Honeywell’s Pilot Advisor for TFE731 and TPE331 engines.