FIKI: Pilots likely recognize the acronym; perhaps so do regular business aircraft passengers. But apparently even those who fathom the translation – Flight Into Known Icing approval – don’t always appreciate the limitations of the anti-icing systems that underpin an aircraft’s approval for FIKI operations.

Dave Higdon  |  01st October 2010
Back to Articles
Dave Higdon
Dave Higdon

Dave Higdon is a highly respected, NBAA Gold Wing award-winning aviation journalist who has covered all...

Read More

Flying Safely:
Ice - in the galley only- please.

FIKI: Pilots likely recognize the acronym; perhaps so do regular business aircraft passengers. But apparently even those who fathom the translation – Flight Into Known Icing approval – don’t always appreciate the limitations of the anti-icing systems that underpin an aircraft’s approval for FIKI operations.

And failing to recognize those limitations – as well as failure to appropriately act on icing encounters – can quickly turn an otherwise routine mission into one with the most-negative of descriptions: not merely remarkable but unforgettable for the feeling that you might not escape intact. Icing protections systems aside- no other meteorological condition poses as insidious a risk as that posited by lengthy encounters with icing conditions.

Not only do the risks bear remembering by flight crew- but also by those whose lives have been entrusted to the flight crew – those who would pressure or otherwise encourage the abandonment of sound judgment in the face of “We’ve-Done-It-Before-and-Survived” claims - or any other form of “Get-There-itis” With little warning and virtually no accompanying sound- ice build-up can leave a crew with an airplane impossible- not merely difficult- to control - one more weighted down by frozen water than available power can counter.

The autopilot in the light jet signaled the pilot of an out-of-trim condition which initially confounded the pilot holding in a steady rain. After descending to 12-000 msl from FL370 on a cold winter’s night- the single pilot of the jet also noticed that a couple of engine indications mismatched. That’s when the pilot switched on the landing lights and discovered that the assigned altitude left the jet at the ragged bottom of an overcast layer – a layer the pilot previously believed they cleared on the let-down.

Activating the anti-ice system and manually cycling the pneumatic boots seemed to help- but the pilot’s concerns rose further when the airplane needed more power to maintain altitude.

Still 60 miles out from the destination and stuck in a queue of other airplanes holding in the weather- the pilot keyed the mic and asked Center for a lower altitude – a request that drew the initial- expected “Stand by…” response. As the pilot waited- already concerned about the aircraft’s true condition- the pilot disengaged the autopilot and quickly learned that the jet wanted to roll hard to its right – still needing more power to hold altitude.

That’s when the bad news arrived- Center responding- “Unable due to traffic.” At that point the pilot felt continuing the hold to be unwise; with a runway of suitable length just a few miles back- the pilot again keyed the mic and this time told the controller of the need to divert- that the airplane was picking up ice and getting heavier and more difficult to fly.

“It’s raining- we’re in and out of clouds- OAT is 28-” the pilot reported. “Were coming down if we continue at this altitude; diverting to…”

In fact- the pilot had already started the turn back and the controller approved the descent as the jet rolled out on a direct heading to the alternate airport. Remembering instructions about using higher approach speeds and eschewing flaps- the pilot ran through the calculation to arrive at a new approach speed and runway numbers for a no-flap landing.

From that point the only additional eventful element of the flight came when the pilot stepped out of the cabin door to gaze upon an ice-coated door frame; two inches thick- built up on the fuselage- aft parts of the wings- and clinging to engine nacelles just beyond the reach of the heated inlet.

With ice coating the ramp- deposited as the storm passed through an hour earlier- the FBO sent a golf cart – its rear wheels adorned in traction chains. While riding away from the small jet- the pilot noticed how the wings and tail components also carried a sheen of ice- the thick stuff cleared by the anti-ice gear. In nearly two decades of flying- the pilot recounted- other icing encounters also became suddenly sinister- as opposed to an inconvenience.

Via the mix of sub-freezing air- rainfall and moisture still existent in the clouds- ice formed so quickly and so universally that continuing – even with clean wings and lifting surfaces – would have subjected the fuselage to hundreds of additional pounds with the weight of frozen water. “At some point- the weight would have overwhelmed the airplane and we’d have gone in like a speared olive dropped into a martini glass-” the pilot explained. “How close we were- I can’t say; but closer than I ever want to be again.”

Whether smooth ice- rime ice- rough frost or smooth frost- airframe icing poses a threat to even aircraft equipped with the best in anti-ice gear because- so far at least- no anti-ice system works to protect the fuselage - and the bigger the fuselage- the bigger the potential problem – a problem with demonstrably lethal tendencies.

Understanding the threat- how to avoid it and how to deal with it can save even the most well-protected airplanes out there.

Fall is here - a season marked by the wondrous color palette Mother Nature provides as leaves change and weather patterns shift people from complaining about the heat of summer to grumblings about the cold of the winter that will follow.

According to a study of 19 years of icing accidents by the National Transportation Safety Board- 81 percent occurred between the beginning of October and the end of March. And icing accidents amounted to about 12 percent of all weather-related accidents- according to research from the AOPA Air Safety Foundation. Do we have your attention yet?

That means the ensuing six months offers increasing opportunities to encounter icing conditions:

• Liquid moisture in the air;
• Airframe temperature below freezing;
• Airspeed below the point where air-generated skin friction can offset below-freezing ambient temperatures.

Further: The label “liquid moisture” should not be confused with “visible moisture-” though that’s how we tend to think of icing conditions: in air with “visible moisture” like clouds- fog- mist- and rain. Icing can also form on a chilled airframe flying through high-humidity air that’s not technically “visible.” Evaporated water molecules strike a cold surface- condensing into “visible” moisture and- thanks to the sub-freezing temperature- freeze.

Generally- the high-flying business jet faces little threat in cruise; at the altitudes most business jets use- any moisture in the air is likely to already be frozen – microscopic ice crystals floating in the sky look much the same as liquid moisture in a cloud. But business turbine aircraft always use ice-prone altitudes to get to cruise altitude and back to a runway. The main threat to the typical business turbine plane arises when climbing from take-off to interim altitudes en-route to cruise or when descending and slowing down for the approach. Water- still liquid- strikes the airframe – one below freezing – and the water freezes.

Super-cooled water droplets – those which remain liquid at temperatures well below freezing – can be particularly nasty because they tend to be large droplets and- once they splash onto super-cooled metal- freeze quickly enough to maintain a somewhat cohesive shape. Thus- the water doesn’t have a chance to sheet or form a thin layer before freezing - and the result can be the roughest iced surfaced that nature produces – rime ice with an attitude.

With statistics showing that about one in eight weather-related accidents are due to airframe ice- flight crew should need little encouragement to pursue their best-available avoidance techniques – or- if avoidance is impossible- their best escape efforts.

Following- we look at how ice can hurt- the conditions conducive to ice accretion- the types of ice that pose risks- and how to plan to avoid (or escape- if avoidance fails). First- ice growing on wing and tail surfaces quickly and dramatically alters the aerodynamics of that surface - and that means that supercritical airfoil becomes superbly less efficient- not to mention less predictable and stable. Additionally- the extra drag of the changed shapes can make holding speed and altitude difficult on the available power.

Of course- icing is the reason manufacturers install anti-ice equipment on the nacelle inlets of jet and propjet engines; ice grows as more moisture passes- and that inlet can shrink to a point that the engine begins to starve for air. As noted- ice can grow out of humid air- from super-cooled raindrops- from super-cooled suspended droplets- or from super-cooled full-size water drops.

Second- ice is dense; less dense than water - which is why ice floats in our drink glasses and in the ocean - but otherwise- you wouldn’t want to carry around a gallon just for fun – not at more than eight pounds per gallon. Let’s put this into airplane terms:

One cubic foot of water weighs more than 62 pounds- meaning a layer of ice one inch thick spread over 12 square feet adds just under 62 pounds to the airplane. Now think of the square footage of a typical jet wing… the weight of an inch of ice can add more than 2-000 pounds from building-up only on 200 square feet of wing; the weight of that inch increases with wing areas. In fact- because ice accumulates on both the top and the bottom of the airfoils- it can run double the per-square-foot weight of an inch of ice. Add the square footage of the fuselage and tail surfaces- and adding another 1-000 pounds in ice takes a relatively small plane.

You can probably start to appreciate the problem potential with larger jets. An inch of ice can put an airplane significantly above gross weight and keep it above gross weight at landing- even with light tanks. Accumulate more than an inch of ice- and all bets are off as the weight issue increases proportionally.

Now combine the two problems – airfoil deformation and extreme weight- which compounds into other issues: higher stall speed- higher landing speed- higher landing weight- higher fuel consumption- slower response and an inability to hold altitude regardless of the power available.

Ice on the horizontal stabilizer can actually cause that surface to stall- sending the airplane into a rapid- severe pitch-down movement. In essence- there are only a few areas in which ice and airplane belong together – and those places include the galley- the drink glass and the food cooler!

As with other forms of undesirable weather- such as thunderstorms- the best encounter where airframe icing is concerned is no encounter at all. Hence- training to look for - and plan around - icing conditions offers the best chance of avoiding a chilling encounter.

It’s not enough to simply brief the departure and arrival airports without looking seriously at conditions in between. You want to know of any icing forecasts for the route- as well as the points of origin and destination; check cloud-top and ceiling forecasts- areas of above- and below-freezing temps- both on the ground- and between ground and cruising altitude.

Next- be especially wary if you see below-freezing temperatures at your destination and at ground level; it’s going to be colder higher- which means a descent through clouds will work its icing magic on your airplane. If the route shows that you can’t avoid icing conditions at altitude- look for a different route that avoids such an encounter.

Avoid slow climbs or descents through clouds at below-freezing temperatures; icing is pretty much assured. Mentally create an escape plan with an escape route for different points of the trip – remembering that generally the easiest and smartest way out of icing is back the way you just came- where there was no icing. In other words- be prepared to make a 180-degree turn.

Turn on all anti-ice gear the instant you think icing is happening or is merely possible. Avoid long holds in visible moisture and in below-freezing air; remember- anti-ice works only on airfoil surfaces- engine inlets and- if so equipped- propeller blades. That leaves the entire fuselage subject to collecting ice – as well as the possibility of the wings and tail surfaces not completely shedding ice when the accumulation is fast and furious.

Factor in the need for extra fuel- both for the possibility of needing to divert- and also for higher fuel consumption if the airplane begins to ice-up. Plan for higher speeds across the board - whether maneuvering- approaching or landing. And remember that stall-speed increases with both weight and the mis-shapen airfoils. If you’re departing with icing at your departure airport- be sure to indulge yourself in a stop at the de-icing shop; trying to take-off with even polished frost can be a prescription to disaster.

Finally- review the handbook for your airplane and any specific instructions for iced-up operations. For example- some aircraft do better with ice and no flaps on landing. Others may recommend disengaging the autopilot when you’re icing-up to help avoid the sudden surprise of the servo clutch letting go due to an excessive load one way or another.

According to the FAA- the AOPA Air Safety Foundation and several other sources- even the presence of frost poses risks to the flight performance of an airplane. Where once the FAA used to approve of the practice of “smoothing” or “polishing” the frost to a smooth surface- now the agency and safety authorities recommend losing the frosty layer altogether.

From the outside-the-cabin perspective- the only good ice is no ice at all; not frost- not polished frost- not rime ice- smooth ice- irregular ice- whatever its origins. And for those days when the destination is absolutely inaccessible without an icing encounter- that’s the time to gently tell the folks traveling with you to gather around a hot drink and share in the cold Tales from the FIKI Side. You can be sure they’ll find those stories chilling enough to appreciate the delay!


Cessna Citation XLS+ 1
Cessna Citation XLS+
Price: USD $7,400,000
United Kingdom
Daher Kodiak 100 1
Daher Kodiak 100
Please call
Bell 412EP 1
Bell 412EP
Make offer
Bombardier Global Express XRS 1
Bombardier Global Express XRS
Make offer
loder image