Cold weather operations, snowy environments and the related issues always pose special challenges for operating pilots. Ice and snow accumulations on aircraft, ramps/taxiways and runways are of particular concern, especially during takeoffs and landings. While it is possible to safely operate GA/Part 91 aircraft in these conditions, there are certain procedures and regulations you should reacquaint yourself with prior to Ol’Man Winter’s arrival this year.
A Little Physics, Plus Some Regulations Equal the “Clean Aircraft Concept”
Test data indicate that ice, snow, or frost formations having a thickness and surface roughness similar to medium or coarse sandpaper on the leading edge and upper surface of a wing can reduce wing lift by as much as 30 percent and increase drag by 40 percent. Of course, thicker or rougher frozen contaminants can have increasing detrimental effects on lift, drag, stall speed, stability and control, with the primary influence being surface roughness located on critical portions of an aerodynamic surface.
These adverse effects on the aerodynamic properties of the airfoil may result in sudden departure from the commanded flight path and may not be preceded by any indications or aerodynamic warning to the pilot. Therefore, it is imperative that takeoff not be attempted unless the PIC has ascertained, as required by regulation, that all critical surfaces of the aircraft are free of adhering ice, snow, or frost formations. This forms the basis for 14 CFR 91.527. In part the regulation says “…the aircraft must be free of all frozen contaminants adhering to the wings, control surfaces, propellers, engine inlets, or other critical surfaces before takeoff’…”
Critical aircraft surfaces, which must be clear of contaminants before takeoff should be described in the aircraft manufacturer's maintenance manual or other manufacturer-developed documents, such as service or operations bulletins. Generally defined, critical aircraft surfaces include: Pitot heads, static ports, ram-air intakes for engine control and flight instruments, other kinds of instrument sensor pickup points, fuel vents, propellers, and engine inlets, wings, empennage, and control surfaces. Fuselage upper surfaces on aircraft with center mounted engines.
More than 30 factors have been identified that can influence whether ice, snow, or frost may accumulate and cause surface roughness on an aircraft. These factors include ambient temperature; aircraft surface (skin) temperature; deicing fluid type, temperature, and concentration; relative humidity; and wind velocity and direction. There is always a need for close inspection before takeoff. GA/Part91 operators are required to conduct a pre-takeoff contamination check prior to takeoff. The “FAA Administrator” may authorize Takeoff with frost under the wing in the area of the fuel tanks, if it can be shown that there is minimal degradation of aircraft performance due to these accumulations. However, under-wing frost that degrades airplane performance beyond a minimal amount is acceptable if the appropriate performance information is provided in the AFM.
AC 120-60B provides an industry-wide standard means for obtaining approval of a Ground Deicing /Anti-Icing Program in accordance with Title 14 of the Code of Federal Regulations.
Part 121 operators require a complete deicing/anti-icing program that includes the training and testing of all personnel involved in the ground-deicing/anti-icing process.
Part 135 requires training and testing for pilots only. Additionally, if a part 135 operator chooses to use personnel other than pilots to assist in the ground-deicing/anti-icing and verification process, then those individuals must receive adequate and appropriate training.
Part 125 requires testing for pilots only; however, other personnel involved in the deicing/anti-icing process must receive adequate and appropriate training.
Part 91/GA, there are no provisions for an approved Deicing/Anti-Icing program. This means that as a private operator the “Clean Aircraft Concept” fits squarely on the PIC’s judgment. In order to use Hold Over Times in lieu of Pre-Takeoff Checks, you must have an approved ground deicing / anti-icing program. The “Hold Over Time” chart produced by the FAA is still useful to you, but they do not relieve you of the responsibility of doing a Pre-Takeoff Contamination Check or the authority to delegate responsibility for that check to a ground crewmember.
The HOT means two different things, depending on whether you have an approved program (121/125/135) or not (91/GA). With an approved program, the PIC may have designated personnel conduct a Post Deicing Check and need not conduct a subsequent Pre-Takeoff Contamination Check if takeoff occurs within the HOT. Without an approved program, The HOT is advisory only. Crews must perform the post deicing check and if conditions are conducive to additional contamination must conduct a Pre-Takeoff Contamination Check within 5 minutes before beginning takeoff.
The Latest Deicing Update from the FAA
In August 2016 the FAA published thier updated de-icing holdover time,HOT guidance for the 2016-2017 winter season. HOT and allowances published last year related to the accelerated degradation of fluids on flaps/slats in the takeoff configuration, including a 90-percent adjustment, remain unchanged for this season. Click here for a link.
THE LATEST DEICING UPDATE FROM Transport Canada
Obsively the Canadian's are pretty much an expert when it comes to winter time flight opsrations. Click here for Transport Canada's hold over tables.
What Can a Private/GA Operator Use for More Information?
Here are a couple of links to NASA sponsored training on aircraft icing and a checklist for pilots on the subject:
Here are some useful definitions found in AC 120-60B when describing deicing checks:
A check of the aircraft’s wings or representative aircraft surfaces for frozen contaminants. This check is conducted within the aircraft’s HOT and may be made by observing representative surfaces from the flight deck, cabin, or outside the aircraft, depending on the type of aircraft and operator’s FAA-approved program.
Pre-Takeoff Contamination Check
A check conducted after the aircraft’s HOT has been exceeded to ensure the aircraft’s wings, control surfaces, and other critical surfaces, as defined in the certificate holder’s program, are free of all frozen contaminants. This check must be completed within 5 minutes before beginning takeoff and from outside the aircraft, unless the certificate holder’s FAA-approved program specifies otherwise.
Post Deicing Check
A check, after deicing application, to ensure all aircraft surfaces are free of frozen contaminants.
Listed below here are just some of the subjects that an approved commercial operator’s program is required to cover. These items are neither comprehensive nor exclusive, and the POI may require additional criteria.
- The requirement for a thorough preflight inspection in extreme temperatures
- The effects of increased viscosity of fluids in cold temperatures
- The hazards associated with wet snow or slush in wheel wells when entering freezing temperatures
- Ice on tail and recovery techniques in stall
- Techniques and procedures for braking, steering, and reversing with water, slush, or snow on taxiways and runways
- Deicing and anti-icing procedures and equipment for frost, ice, or snow removal from airfoils, control surfaces, and static ports
- A description of landing surface conditions and appropriate braking action.
- Emphasis upon use of engine anti-ice, both on the ground and in flight, when engine icing potential exists.
- Abnormal engine instrument indications, such as EPR, fuel flow, or compressor speeds should be addressed
- Crews instructed on the use of engine heat whenever any doubt exists as to its possible need.
- Cross-checking engine parameters during takeoff with provided data. This cross-check may include such items as fuel flow or compressor speeds (N1)/(N2) being compared with thrust setting or EPR commanded.
- AC 120-60B, Ground Deicing and Anti-Icing Program
- Transport Canada, Guidelines for Aircraft Ground Icing Operations, 2nd ed
- ICAO Doc 9640, Manual of Aircraft Ground Deicing/Anti-Icing Operations
- EASA Safety Information Notice, 2008-29, Ground Deicing/Anti-Icing of Aeroplanes
- EASA Safety Information Bulletin, 2010-26, Potential Performance Degradation of Anti-icing Fluids – Reduced Holdover Times
- 1. Part91/GA Operators do not have an approved program
- 2. Holdover times are guidelines and advisory only
- 3. Icing conditions can change from inspection time to actual Takeoff
- 4. "Clean Aircraft" conditions are the requirement prior to operation