This story begins when I was about 11 years old and my dad, a career Air Force Pilot, was stationed in a backwater – at least in those days – called St. John’s, Newfoundland. In 1949, Labrador and the island of Newfoundland were combined to become the easternmost province of Canada. Before then, it was a British colony and in the mid-1950s when we lived there, the world was passing it by. St. John’s was the province’s largest city and became its capital. Fishing in the Eastern Atlantic and in an area what as known as Grand Banks was its primary industry.
In 1901, on what is now known as Signal Hill, Marconi set up the first radio station to transmit and receive radio signals to and from the U.K. And, in June, 1919, John Alcock and Arthur Brown took off from a field near where the current airport is and made the first non-stop flight across the Atlantic in a modified World War I bomber called a Vickers Vimy. When Lindbergh made his solo crossing, he flew past Marconi Tower. It was his last sighting of land until he crossed the Irish coast and the act was immortalized in the move Lindbergh starring Jimmy Stewart. During World War I and II, St. John’s and its deep, protected harbor got its fame as one of the jumping off points for convoys headed to Europe.
When we lived in St. John’s, the Air Force had two bases, one on the eastern end of the island called Torbay –now St. John’s International Airport– and Harmon AFB in Stephenville, at the southwestern end of the island. The Navy had a base on the southern part of the island at a small town called Argentia where Churchill and Roosevelt met in August 1941.
So much for history… One of my many memories of living in Newfoundland happened one evening. Earlier that day, my dad took off in a C-47 on a flight to Harmon and Argentia to do what is known as “flight check” the airfields’ instrument landing systems (ILS) and their ground controlled approaches or GCAs. The Air Force had (or maybe still has) specially equipped airplanes that could evaluate the quality/accuracy of the radars for the GCAs and the signals for the ILS’s. After they were “flight checked,” they were certified for instrument approaches.
When he returned, the twin-engine C-47 taxied up in front of base operations. My mother and I walked onto the ramp and I ran to greet my dad. He came out of the back door with a long screwdriver in his hand, a grim expression and didn’t acknowledge me. It was as if I didn’t exist.
Dad climbed on to the C-47’s large main tire and jabbed the leading edge of the wing several times. A huge block of ice fell down and it had a large crescent that was the shape of the leading edge of the wing. Like a man on a mission, dad marched past my mother and me and headed into base operations.
I followed and watched him dump the block of ice on the weather forecaster’s desk. It landed with a loud clunk. He banged down the screwdriver and glared at the weatherman…. “Whatdayya mean no ice?” Dad stormed out leaving a grim forecaster with a block of ice that probably weighed about ten pounds melting on his counter.
Years later, when I started flying, I asked him about that night. He said that what made him so mad was that the forecaster had told him, during their weather brief, that there was virtually no chance of airframe icing that night. He’d spent six hours in the air battling rime ice. The chunk of ice was proof that the forecaster was wrong!
That was my introduction to the dangers of ice forming on the wings and fuselage of an airplane. Little did I know later, I would be saying those same words!
Fast forward to 1977. I was droning happily along in a twin engine Piper Aztec flying from Lock Haven, PA to our destination – Tulsa International Airport. It was cold and snowy when we took off from the headquarters of Piper Aircraft in north central Pennsylvania. Hundred knot headwinds reduced our groundspeed to, at times, 80 – 90 knots and it took us over four hours to get to Nashville, TN where we stopped for gas.
When we took off again, the FAA’s forecast for Tulsa was overcast with the cloud bases reported at one thousand feet and layers of clouds up to eighteen thousand feet. The forecasted noted that it was supposed to start raining two hours after our planned arrival AND when asked, said there very little chance we’d encounter any icing. We took and climbed to our assigned altitude of twelve thousand feet was we headed west.
A little bit of meteorology will help those who are not familiar with the phenomenon of ice forming on airplanes. I could simply say that ice and airplanes, particularly general aviation airplanes is not a good mixture and you would ask, reasonably so, why? What follows is a distillation of the essence of what is known about icing.
Airframe ice attaches itself to the airplane or helicopter when you have three conditions:
- Visible moisture, i.e. clouds, rain, snow, etc.;
- A “supercooled” surface such as the wing, fuselage, propeller or rotor blade of a helicopter; and
- The ambient air temperature is in the “right” range for icing.
Airframe ice comes in three types. Rime is a medium gray, gloppy mix, until it freezes solid when it becomes course and rough. It normally starts forming on the leading edges of the wings, air intakes, antennas, the nose of the plane and the windscreen. Its color makes it visible, even at night and forms at minus fifteen degrees Centigrade (5° F) to minus twenty Centigrade (- 4°F).
Clear ice is much more insidious. It is called clear because it looks like a shiny new finish on the airplane and is almost impossible to see at night. Clear ice coats everything and builds very, very quickly. It starts to cover the skin of the airplane between minus ten degrees Centigrade (14°F) to plus two degrees Centigrade (36°F) to
Rime ice changes the shape of the wing’s airfoil. The result is additional drag, reduced lift and worst all, increased airframe weight. More weight and drag mean you need more power to maintain airspeed and altitude and that means you will be burning more fuel.
Clear ice forms very quickly and adds weight just as fast. Think of clear ice as spraying the airplane with a thick coat of paint or freezing rain coating a car or road. Suddenly, one has to add power to maintain altitude and airspeed.
The third type – mixed ice – is even worse. It is a combination of rime and clear and creates drag faster and adds weight quicker. The good news it that it starts attaching itself to the airplane in the very narrow range of between minus ten degrees Centigrade (14° F) to minus fifteen degrees Centigrade (5°F).
Ice increases the weight of the airplane and increases its stall speed. Rime ice also changes the aerodynamic characteristics of the wing. Pick-up enough ice and the airplane will start to descend because you don’t have enough power to maintain altitude. Or, it will suddenly stall and you wont have enough control to recover.
Suffice it to say, one should avoid conditions in which airframe ice could occur. A discussion of anti- and de-icing systems is beyond the scope of this story other than to mention “hot props” on the Aztec. These are propeller blades that have an electrical heating element on the leading edge and when working, ice can’t stick to the blades.
The other pilot, who had flown air cargo in the Northeast before joining Piper, had seen ice before and so had I. John (I wont use his last name) is now one of the top three executives in one of the largest airframe manufacturers in the world. When we took off from Nashville, we were confident we would get there ahead of any risk of icing by staying in air cold enough so ice wouldn’t form and then descending quickly through the air warm enough for icing conditions.
The winds hadn’t abated much at any reasonable altitude so we stayed at 12,000 feet and instead of covering the ground at 180 – 190 knots, we were poking along at a ground speed of 130ish. As we crossed into Oklahoma, the clouds thickened and at our altitude, we were out of the icing temperature range. About every hour, we checked with the FAA’s Flight Service Stations to see if they had any reports of icing. There were none.
Both John and I knew that as we descended it would get warmer and the chance of picking up some ice would increase. Before we started down, we listed to the recorded information for Tulsa’s weather and it said nothing about rain or snow. The weather was was overcast with a 1,000 foot ceiling and a temperature of thirty-five degrees Fahrenheit or one degree Centigrade. There was no mention any precipitation or local icing conditions. On our initial contact with the approach controller, John asked if there were any reports of icing and were told that there were none in the Tulsa area.
The rule of thumb is that the air temperature increases or decreases by two degrees per thousand feet as you climb or descend. As a precaution, we turned on the electric prop-deicers and the heaters for the pitot static system when we completed the descent check list. The electrical heating elements in the pitot static system that includes the airplane’s airspeed, altitude and vertical speed indicators should keep any ice from forming.
I remember that as we were passing ten thousand feet, the temperature was fifteen degrees Fahrenheit. It was too cold for ice to form.
Since I was the pilot in command and flying the Aztec, John monitoring the instruments and looking out side for, you guessed it, ice. By the time we passed eight thousand feet, the temperature probe for the outside air temperature probe had a ball of rime ice. I glanced at the wing and could see ice starting to form.
I asked the approach controller if we could descend as soon as possible to two thousand feet. He had to clear some traffic, but about a minute or two later, he cleared us to descend at pilot’s discretion to two thousand feet.
By this time, the windshield was coated with rime ice. Out the side window, I could see ice starting to block engine cooling intakes. Rather than ease off the power and lower the nose when I started down, I trimmed the nose down to maintain descent rate of between 500 and 1,000 feet per minute down and let the airspeed increase. Speed will get us through the icing layer faster and be helpful if we pick up a load of ice.
The vertical speed indicator had crept up to almost two thousand feet per minute down without me doing anything so I raised the nose and added power to reduce it. By now, the rime had turned to mixed ice and the windscreen was opaque. The small heated section of the windscreen in front of me had been overwhelmed by ice.
By the time we passed about four thousand feet, the beat of the propellers tossing off chunks of ice was just part of the noise. They started slinging bits of ice around six thousand feet. The sound of the first few banging off the plates on side of the fuselage designed to take this abuse was surprising at first, and then I ignored, concentrating of flying the airplane and maintaining my instrument scan.
As we leveled off, the Aztec mushed and wallowed. It was struggling to stay in the air. We were indicating about 150 knots instead of 180 and to maintain our assigned altitude, I had to go to full power! Even then, I had to trade a little airspeed to maintain two thousand feet. Thankfully, the ILS glide slope locked on and we did the landing checklist. When my co-pilot put the landing gear handle in the down position, there was a groan and then a cracking sound before the motors got the gear doors open and the wheels down.
With the wheels hanging out and the extra drag, the Aztec started to descend. With full power on the airplane, we were barely able stay on the glide slope. There was no way the airplane was going to climb or fly level. The question in my mind was I going to make it to the runway that I couldn’t see?
Flaps weren’t an option. First, I wasn’t sure if they would go down and what if one side went down and the other didn’t. Second, if they went down, I had no idea of what they would do to the way the plane flew.
Mixed ice had worked its way past my side window. Glancing over John’s shoulder confirmed what the tower was now telling us. They had freezing rain!!!
Gently, I herded the Aztec down the glideslope. Flying it would be imply that I was in full control. I wasn’t. We – the Aztec and I – had come to an understanding. It would go in the general direction that I wanted and we agreed to land on the runway!
At about 700 feet above the ground, John looked out one of the cabin windows and said we had popped out of the clouds. I kept flying the ILS and kept the needles centered hoping that the flight check aircraft had them calibrated. There was no other choice. I remembered my dad and all the flight check flights he made in Newfoundland, Labrador and Greenland flashed through my mind. He made it and so will I.
I didn’t look up because there was nothing to see. The windscreen was covered with gray mixed ice. At a hundred feet, John said we just crossed the runway threshold.
Luckily, we had a radar altimeter. I had set the bug so it would warn me when we got to twenty feet off the ground. It went off and I raised the nose slightly and the Aztec shuddered. It stalled and landed with a thump on the runway. The airspeed indicator said we were going about 100 knots. The normal landing speed is about 70!
The Aztec banged down hard enough so chunks of ice fell off the plane. One that came off was in front of the heated portion of the windscreen. Now I could see to taxi and the nose of the airplane. The windscreen had two solid inches of mixed ice!
As soon as I was on the runway, I pulled the throttles back to idle and taxied to the fixed base operator to park. When we pulled in, I could see the trail of chunks of ice we left on the taxiway that looked like breadcrumbs. Out on the runway, there was a bigger pile where we touched down.
Both of us got out and stood there in the freezing rain looking at the Aztec. It was covered with at least an inch of clear ice on the wings and two to three inches of mixed ice on the leading edge of the wings, elevator and rudder and nose. I couldn’t have lowered the flaps if I wanted to. And, I didn’t have full movement of any of the control surfaces. Later, we guestimated, based on the power settings, that we carried somewhere around 1,500 to 2,000 pounds of frozen water. John admitted that he’d never seen so much ice on an airplane. Neither had I.
At dinner that night, I told John the story about my dad and his ice covered C-47. Now I knew what he was so mad. It happened to me too. Two people – the weather forecaster in Nashville and the approach controller all said there were no reports of ice. So we forged ahead. The moral of our two stories is that forecasting icing condition is an “inexact” science. Sometimes there’s ice there and sometimes, even though the conditions are ripe, there isn’t. Unfortunately, often you don’t find out ice is there until you fly into it.