There’s Ice and Then There’s ICE!

As I write this story, it is early March 2024 when I often think about a flight in a Piper Turbo Aztec that involved icing way back in March 1978. My logbook shows I took off from Louisville International Airport (now Mohammed Ali International), flew to Will Rogers International Airport in Oklahoma City, OK.

For those of you who do not know a Piper Turbo Aztec from a hole in the wall, it is a light twin-engine airplane that seats six; has a large cargo compartment in the nose and a baggage compartment aft of the third row of seats. Originally designed in the 1950s by the Stinson Aircraft Company, the plane was initially built and sold as the Piper Apache until Piper swapped out the 150-hp Lycoming O-320s engines for 250-hp Lycoming O-540s and called the plane the Piper Aztec.

The Aztec kept original wing design along with the carburetors on the non-turbocharged engines. To improve its high-altitude performance, Piper installed turbocharged TIO-540s that produced 250 horsepower and called it a Turbo Aztec. The turbocharged Aztec easily cruised at 180 knots at 12,000 with four people, some baggage, and full fuel. If you took off in an F model Turbo Aztec with 177 gallons of 100 octane fuel (thanks to the optional 40 gallon “long range tanks”), at 12,000 feet, the Turbo Aztec burned about 16 gph per engine at 75% power. This allowed for five hours of flying with a 45-minute reserve.

When I took off from Louisville in a PA-23-250F Turbo Aztec, the weather in Oklahoma City was 3,000 overcast, and the temperature on the ground was 34 degrees Fahrenheit. From a go-no-go perspective, the weather was marginal, and the forecast did not call for icing, even though the conditions for icing did exist. The FAA weatherman said “airframe ice was possible” which it was. Experience also told me that forecasts for icing were hit and miss, and I decided to launch. Afterall, I had an important meeting in OKC.

For those of you who fly, know that icing can occur when the temperature is 0 degrees Centigrade (32 degrees Fahrenheit) or colder, there is visible moisture and a supercooled surface. Clouds – even if there is no precipitation – qualify as visible moisture, and flying airplanes provide the supercooled surface.

Those who fly business and military jets and airliners use high rates of climb and descent that take the plane up through icing layers in seconds. And most have a surfeit of excess power to enable the plane to easily climb out of icing conditions. This isn’t true with many piston-engine General Aviation airplanes in which icing is evil. I’d encountered ice several times while flying helicopters in the Navy and in general aviation airplanes. Each time, I managed to climb above or descend below the altitude where the icing was occurring.

Enroute, I radioed a Flight Service Station and learned the weather in OKC was deteriorating as forecast. The ceiling was now down to 2,000 feet and expected to be around 1,000 feet and the new piece of info from the Flight Service station was that it was now forecast to start raining around when I arrived. At the time, he didn’t have any reports of icing in the vicinity of OKC so I continued the trip.

When instructed to contact Oklahoma City Approach, I’d already been cleared to descend from 12,000 feet (my favorite cruising altitude) to 4,000 and asked the approach controller to let me stay at 4,000. The approach controller said that an airliner landing at OKC had encountered ice between 2,000 and 3,000 feet. I wanted to stay above that altitude until I intercepted the ILS localizer. 

Once I started down toward the runway, my plan was to keep my speed up, descend quickly through the icing and intercept the glide slope. Once below the clouds, and with the runway in sight, I’d lower the flaps and landing gear and land. Will Rogers has two 9,800-foot-long parallel runways so if I landed long, it wouldn’t be a problem. 

There are two kinds of icing. Rime which looks like gloppy snow attached to a wall and clear, which is transparent. Both increase drag, reduce lift, and add weight, a lot of it.

Cleared for the ILS to Runway 35 Right, I double checked to make sure the pitot heat and propeller de-ice was turned while keeping the course deviation needle on the horizontal situation indicator (HSI) centered to ensure the plane was on the localizer. A gentle push and nose down trim lowered the Turbo Aztec’s nose. It accelerated as I descended and almost immediately, the plane started to pick up ice. 

Rime ice appeared first. I could see it on the probe for the outside air temperature gauge and along the leading edge of the wing. Then, passing 2,500, the freezing rain started.

Normally, in the Turbo Aztec, I flew the ILS glideslope at 110 knots, props set at 2,400 rpm, mixture rich, 20 inches of manifold pressure, and half flaps. In a normal approach, I’d cross the runway threshold at about 90 knots, and just above the runway, close the throttles, bleed off some airspeed, flare, and touch down. 

Not this time! The landing gear would be lowered at the outer marker as I started down the glide slope. Full flaps would be selected once I had the runway in sight, but not this time. 

I kept the Turbo Aztec at 140 knots and llmost instantly, the plane was coated with clear ice and began to descend faster from the additional weight and drag. Instead of the 20 inches of manifold pressure and 110 knots I’d normally use, the manifold pressure gauge showed each engine at 30 inches, which is what I needed to maintain 140 knots, stay on the glideslope, and descend at around 500 feet per minute. 

More power would be needed to level off and even more if I wanted to wave off and climb. How much more, I did not know which meant I was committed to landing.

The windshield de-ice couldn’t keep up with the ice accumulation, and the only way I could tell I had descended below the clouds was by looking out the side windows. The altimeter said the Turbo Aztec was descending through 1,200 feet. By the time I popped out of the overcast, I had increased the power to 32 inches of manifold pressure to stay on the glideslope. Max power at sea level was 39 inches of manifold pressure so I was running out of available power.

To see out front, I crabbed the airplane to point the nose to the right to look out the left side window. The maneuver let me see the runway but also increased the rate of descent. I did it twice to make sure I was lined up with the runway centerline as I struggled to keep the ILS and glide slope needles centered. They were the only reference I had to guide me down to the runway.

Once out of the clouds, I triggered the pneumatic boots on the wings. They inflated, popped off some clear ice that was quickly replaced with more from the rain hitting the leading edge of the wing. 

Using flaps was out of the question because while they provided additional lift, they also produced drag, something I didn’t need. And, with the ice on the wings, I wasn’t sure if the flaps on both wings would extend equally. At about one-half mile from the runway, I raised the nose to slow the Turbo Aztec and lowered the landing gear at 120 knots. Three things happened almost at once.

One, the gear came down and the green lights indicating the main mounts and nosewheel had locked in place in the down position came on. That was the only good thing. Two, the airplane slowed dramatically and three, the Turbo Aztec’s rate of descent increased.

Both throttles went to the forward stop for all the power the engines could produce, i.e., 39 inches of manifold pressure. The plane leveled off about 100 feet over the runway threshold at about 120 knots and I could see out the side windows I was over the runway. 

The plane started down when I eased the power back a couple of inches. Close to the runway, I eased back a bit more and raised the nose slightly to flare and hopefully cushion the landing.

Normally, the Turbo Aztec stalls at around 60 knots with full flaps or at about 70 with the gear and flaps up. Today, the Turbo Aztec simply stopped flying somewhere around 100 knots about five feet above the runway and landed with a noticeable thump.

Sheets of clear ice slid off the wings. More came off the fuselage as I closed the throttles and held the nose up to use drag to slow the plane down. Below 60 knots, S-turns down the runway let me see through the cabin side windows where to turn off the runway.

On the taxiway after clearing the runway, I stopped the Turbo Aztec and told Ground Control that I had left ice littering the runway. The pause also allowed me to collect my thoughts and let my knees shake. 

By the time I parked in front of Atlantic Aviation, the temperature had dropped to 320 Fahrenheit, and freezing rain was coating the Turbo Aztec. I didn’t care because I was done flying for the day. 

That night, I lay in bed, unable to sleep. By brain let me know in vivid terms how close I had become to being a statistic and a smoking hole in the ground.

This was a classic case of “get there it is,” and in retrospect, I should never have left Louisville. Confidence in my flying skills as a one who flew helicopters and fixed wing machines day and night and in any weather conditions let me down a path that maybe I shouldn’t have taken. 

In my logbook, along the with the Turbo Aztec’s model and registration number, total and actual instrument flight time, there’s a note in the Remarks block – heavy rime & clear ice. Those five words don’t come close to telling the whole story.

2 Comments

  1. Dave Ayres on April 4, 2024 at 11:21 pm

    Marc,
    Fortunately you were well prepared for something to contend with, but the intensity of the icing coupled with the freezing rain almost exceeded your preparations. You flew the airplane all the way through to the landing. My primary instructor always reminded me to “ Fly the airplane all the way through the crash.” You did great!
    Respectfully,
    Dave Ayres

    • Marc Liebman on April 7, 2024 at 10:15 am

      Thanx. Its odd, but there are some things in my flying career that I still think about. My rationalization is that those memories kept me from doing something similar ever again. Have I flown in icing conditions since then in GA airplanes, yes. Was it intentional, no.

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