At this time of year in the Northern Hemisphere, encounters with ice become a safety focus for both aviators and aviation officials. Notwithstanding their concerns, icing also impacts passengers, and too often they don't understand why - aerodynamics and weight limitations aren't everyone's day-to-day concerns, after all.
The more commonly-discussed icing issue is in-flight icing. The weight added and the altered aerodynamics make any amount of ice accretion unwelcome.
Between speed and altitude, flying in icy conditions carries a decidedly higher degree of risk than trying to taxi on a slippery pavement. The limitation of two-dimensional travel and slow travel speed make a significant difference - and to be honest, passengers are likely to better grasp the issues of ground ice after experiencing their own challenges navigating ice-impacted streets and highways en route to the airport.
The challenges of iced ramps, runways and taxiways are nonetheless capable of keeping aircraft grounded. In the event that a passenger challenges an ice-based âno-goâ decision, citing the aircraft's approval for flying into known icing (FIKI) conditions, remember this point: An aircraft's approval for flight into known icing signals an aircraft's approval for exposure to transient icing conditions.
For the majority of Business Aviation flying with FIKI approval should involve transiting clouds between runways and in-the-clear cruising altitudes at the most. A little explanation to those challenging a âno-goâ or a delay decision should reveal clearly that FIKI is not a solution for what happens to an aircraft's unprotected surfaces when exposed to icing conditions for longer periods of time.
About In-Flight Icing
Speaking as a pilot with more time flying unprotected aircraft than aircraft with anti-ice systems, only one other type of weather engenders a more-rapid escape response than icing conditions: Lightning. At the first hint that we may have entered the âIce Palaceâ we turning for the exit, which may be lower, higher, or a 180 degree turn. At the same time, we reach for the FIKI system.
Systems that underpin flight into known icing conditions â whether anti-ice or de-ice â do a great job fighting ice on the surfaces they protect. Those surfaces are the ones that lift the aircraft; give it directional stability; protect engine breathing; and protect certain other sensors. That leaves much of the airframe unprotected. The fuselage lacks any ice-fighting protection, save for its probes or indicator inputs such as an angle-of-attack sensor or pitot tube.
While the FIKI system happily does its job, an aircraft may keep enough flying surface ice-free to fly close to normally, those airframe sections lacking protection continue to accumulate ice for as long as the aircraft remains exposed to sub-freezing temperatures and moisture. The only solution is to escape â whatever that takes.
Most commonly pilots face transiting icing conditions after departure and on approach. On departure it helps to know where the icing layer stops before departing. Then the pilot can calculate the exposure time to expect and make an informed decision on whether to fly or not. Pilots on approaches should know ahead of time whether the standard terminal arrival (STAR) will take them through icing, and likewise calculate the duration of their exposure.
Pilots should consider refusing a hold that keeps them flying the racetrack in icing conditions â or at least a hold longer than a couple of minutes - before heading to warmer and/or drier airspace. Even getting a straight-through approach can put the aircraft at risk for excess weight due to ice accumulation when the layer is so thick and the ice is accumulating so quickly that transiting a 10,000-foot-thick layer translates to 7-10 minutes picking up ice everywhere unprotected by a FIKI system.
Anti-Ice versus De-ice
Systems capable of qualifying an aircraft for FAA- or EASA-approved FIKI come in two basic forms, each with its strengths and weaknesses. Ideally, a blend of each system's strengths would best serve the flying community, but weight, costs and performance considerations all factor into the choices planemakers make when selecting an airframe-icing protection system.
Anti-ice systems offer a degree of protection against ice forming. In many cases they provide an element of protection for surfaces adjacent to the areas they protect. Heat and weeping-surface technologies stand at the head of this group. Transport-category aircraft typically employ heat for wing and tail surface leading edges to prevent ice formation; the residual heat and temperature change from water run-off help extend their protection area further aft than the immediate leading-edge areas.
De-icing, however, by changing the shape of the leading-edge surfaces, offers a solution excellent for removing ice already formed â as well as helping prevent build-up. The system most-commonly used for this approach is the inflatable de-icing boot that's attached to the leading edges of protected surfaces. Used per the Pilot Operating Handbook, de-icing boots not only remove ice that exists on the leading edges, they also prevent build-up behind where the boots end.
Regardless of the system, however, the limitations detailed remain very much in play, and of concern. Avoidance remains the safest alternative â avoidance by exiting if already embraced.
Traction in Ground Transportation
Unlike most modes of transportation aircraft thrust manifests itself directly from the engine. But aircraft generally lack drive systems in their wheels; they need no wheel-to-ground traction for take-off acceleration, leaving the main reason aircraft tires need traction as directional control. On a slippery surface, an engine can move the airplane in the direction opposite the thrust employed. But without traction between wheels and Earth the pilot faces a major challenge steering the machine â at least until moving fast enough for aerodynamic surfaces to work.
Conditions that sheath ice onto the ground, ramps, runways, hangar doors, tower cabs and tugs also begin to coat aircraft the instant they're exposed to them. Between the traction issue and the exposure issue, dealing with ice on the ground may add lengthy delays to your flying schedule â possibly even forcing a new decision.
The safest decision, in general: Don't fly. Let's look at the two separate issues and what's involved in dealing with them.
A sheet of ice coating a ramp, a taxiway or runway leaves the aircraft free to âweather vaneâ in any winds, with engine thrust and rudder being the only control inputs with a possibility of success. From first-hand experience we can testify to the discomfort of trying to turn a tricycle-geared aircraft off a runway with ice that is three-inches thick, and onto a taxiway leading to a ramp where engine heat melted ice enough to confirm that the three-inch thickness of the runway was better than the four-inch coating on the ramp.
âWe didn't treat the ramps as much as we did the runway,â the FBO manager confessed. âEventually we stopped trying; we could not keep up â and we wanted to save the ice melt to speed solar removal...â The product of a 16-hour ice storm, the coatings not only made ground maneuvering difficult, it also sealed shut access doors to dozens of hangars â and more than a few airplanes left out in the freezing precipitation.
Fortunately, a tug with chains was able to meet us at the intersection of the runway and taxiway; we shut down and let the tug take us to the ramp for fuel. A dozen aircraft-worth of delayed crew and passengers were packed into the FBO lobby, the flight planning lounge, the break room and another room usually used for ground instruction. Some of those lamented that their aircraft were ice-free and clean, ready to go â but, unfortunately, trapped behind ice-sealed hangar doors. Others took turns trying to remove 3 to 4 inches of accumulated ice from the aircraft they had left parked outside the day before. Hair dryers, antifreeze, deicing fluid...you name it, they employed it. But with temperatures headed into single-digit territory some of their tools stopped working.
After five hours they ended their efforts with only one wing cleared â about two thirds of the way...on top. âThis was a waste of time and hypothermia,â one pilot confessed. âThe ramp people warned me â I should've listened and saved everyone the risks of the drive.â
After fueling, the tug gently positioned us into the wind, just off the departure runway, and kindly waited to make sure we'd get an engine start. The OAT was 5 by that point. After a little wind started us sliding toward a runway edge we edged up the power, stepped on the rudder pedal and got the directional correction we needed to align with the runway â and we continued adding power to reach a speed that gave all the aerodynamic surfaces input into our direction. The potential for airborne ice behind us, getting into the chilled night air was a welcome relief from the feeling of no control that accompanied our landing two hours earlier.
Runway Friction Reports
The terminology differs between objective measurements of runway friction and the information delivered to pilots via NOTAM, weather reports and pilot briefings. One reason is that not all airports have the special equipment needed to actively sample the runway. Those airports lacking friction-testing equipment depend on the reports of recently landed pilots.
The ratings used are: âgoodâ, âfairâ, âpoorâ, ânilâ, or some combination of those terms. Pilots should ask for a categorization of braking action should the pilot or airport management use terms other than those foregoing labels. Look for information on the type of problem â ice, snow, packed-snow, slush â and the type of aircraft from which the report originated.
A Citation X may give itself more latitude for a âFairâ surface than a wide-body airliner, even though both could be operating under FAR 23. And in a recent move, the FAA made clear that a report of âNilâ means âZero Braking Frictionâ and that runway should consequently be closed. Landing on an ice rink could be no less appealing than a runway with âNilâ braking friction.
Delay of Game
Remember, itâs better arriving a day late than it being forever lamented that you tried and failed in the face of hostile icing conditions. Maybe the problem is as localized as getting from hangar to runway; maybe it's a problem of transiting icing conditions in-flight â conditions capable of challenging the limitations of whatever anti-ice or de-ice equipment the airplane employs. The issue may be as localized as freeing the airframe from any hint of ice or frost. Maybe the de-icing truck's not yet in service; maybe the fluid is gone â or the heater has malfunctioned.
Leaving with any degree of ice can be as quickly fatal as lingering too long in ice before landing. Neither is an option that any pilot or passenger should accept.
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