Ice: gotcha… in a heartbeat

The flight, in a TBM 700, looked like a piece of cake. The weather appeared good and, in fact, there was no record of the pilot even bothering to get any weather information. There are, however, many ways to check weather without creating a record.

The flight started at Teterboro, New Jersey, and was bound for Atlanta. The sky was clear at Teterboro and there was a surface cold front just to the south. Nearby Morristown, N. J., was reporting ten miles visibility with a ceiling of 20,000 feet. The surface temperature was plus six C.

As is almost always the case in the cold months, there was an Airmet for icing. The current Airmet called for moderate icing to FL200. An earlier one had the same but with the top of the moderate icing at FL180.

Pilot reports told a grimmer tale. In the time before takeoff, there had been reports of severe icing from a Citation and an MD-83. One report put the condition between 13,000 and 14,000 feet; the other between 14,000 and 16,500 feet. One of the crewmembers of the MD-83 said it was the worst icing he had seen in 38 years of flying and that he had never seen ice accumulate so quickly.

Severe icing PIREPs

The accident airplane flew through an area where three other airplanes had reported severe icing (graphic from NTSB).

There were definite warning signs but nobody knows whether the pilot was aware of any of this.

The tendency when you are flying a high-performance airplane like a TBM 700 is to head out, planning to vault up into the sunshine in no time at all. This pilot had filed for Flight Level 260 which would be well atop the icing covered by the Airmet.

When the airplane was passing 8,000 feet for 10,000 feet, the controller cleared it to 14,000 feet and advised of moderate rime icing from 15,000 to 17,000 feet with light rime ice at 14,000 feet. The controller asked the pilot to advise if the icing got worse and the pilot responded, “We’ll let you know what happens when we get in there and if we could go straight through, it’s no problem for us.”

Ten minutes after the pilot had called ready for takeoff, the flight was cleared to 17,000 feet where the pilot was told light icing would be encountered. The pilot reported that he was entering instrument meteorological conditions when climbing between 12,800 and 12,900 feet.

When the airplane was at 16,800 feet with a groundspeed of 101 knots, the pilot said “Light icing has been present for a little while and a higher altitude would be great.” Not many seconds later, the pilot reported, “We’re getting a little rattle here can we ah get ah higher as soon as possible please.” Twenty-five seconds later, the pilot was cleared to FL200. A minute and nine seconds after that, the airplane reached an altitude of 17,800 feet before it turned left and entered a descent. Twenty-one seconds later, there was a final abbreviated transmission that included the word “declaring.” The final radar return, less than a minute later, was from 2,000 feet. That was only about 17 minutes after the pilot reported ready for takeoff.

Witnesses reported seeing the airplane descending at a rapid rate, shedding parts, and a wing was reported as missing.

A Bombardier CRJ crew operating in close proximity to the TBM 700 reported that their wing anti-ice system could not keep up with the ice accumulation and that 2.5 inches of ice collected on protected surfaces and four inches on unprotected surfaces, all in about five minutes.

In its infinite wisdom, the government approves properly equipped airplanes for flight in icing conditions and then defines severe (or heavy) icing as that which can’t be handled by deicing equipment.

TBM crash

The TBM broke up at low altitude, probably after a spiral dive, and scattered parts over a wide area.

The NTSB’s probable cause: “The airplane’s encounter with unforecasted severe icing conditions that were characterized by high ice accretion rates and the pilot’s failure to use his command authority to depart the icing condition in an expeditious manner, which resulted in a loss of aircraft control.”

I was talking with Mac McClellan about this. Between us we have flown well over 30,000 hours, most of it IFR, and we have seen a lot of ice while flying some of the frostiest routes in the eastern United States. But between us, we came up with only a few truly memorable ice encounters. That would be one where you could hear the angels singing. That we both survived is self-evident and what we learned was you need to go as fast as possible while getting out of ice even if it means sacrificing altitude. We also learned over the years that there is a lot of ice that can be flown but you do have to pick and choose and always have an “out.”

Which brings us to the TBM 700 pilot: He had reported 1,400 hours on his last medical application. That doesn’t qualify as inexperienced, but there’s no question that there was much out there he hadn’t seen yet. There were stern warnings about ice in the pilot’s operating handbook including word that ice could degrade the performance and controllability of the airplane. Mention was also made of ice forming aft of the protected surfaces. He had likely seen some ice before and dealt with it handily but on the fateful day he found the worst possible ice scenario. Such is rare but it does happen.

There was plenty of ice-free air down below so there was an out but his mind was on climbing and this was pushed too far. Following a low-speed loss of control, the airplane apparently entered a spiral dive, which is characterized by an out-of-the-envelope, high airspeed, high-g, steep bank with the airplane corkscrewing toward the ground at a rate of descent well in excess of 15,000 feet per minute. A pilot would have to understand the nature of a spiral dive as well as the only possible path to a successful recovery to make it through that.

I’ll tell you the theoretical recovery procedure in a bit. Rest assured, it is not taught.

The last two-thirds of the final spiral was likely clear of clouds with that recovery theoretically possible. For a relatively inexperienced pilot, though, it would be akin to trying to put the proverbial egg back together.

I wrote about a King Air accident that occurred many years ago where the overloaded airplane in climb picked up such a load of ice aft of the deice boots that the airplane simply wouldn’t go on any more. This pilot remained more or less in control of the airplane but the impact was too much for the occupants.

I think it was after this accident that manufacturers started publishing a minimum speed in icing in the POH of airplanes with approved equipment.

Over the years there have been other en route icing accidents, almost always characterized by a loss of control. In reading the reports many of the control losses seem to stem from the pilot being distracted by the icing, to the neglect of flying the airplane.

Ice on wing of turboprop

Boots are nice, but should only be used to get out of icing conditions, not to linger in them.

The more common icing accident comes after the pilot gets out of the ice and is maneuvering for landing. It is a given on most airplanes that flaps are not to be used with ice on the airplane and that you need a lot of extra speed on the approach. Apparently some pilots don’t take this seriously enough.

How much extra speed is enough? I flew a severe-ice simulation in a Cessna 208 (Caravan) simulator a while back and it illustrated the challenge found here. With the boots firing away almost continuously and with a determination to maintain a safe airspeed (I think I picked 140 knots) I got the airplane squared away on the ILS with the glideslope intercept coming at about the time the airplane was going to start down of its own accord.

In a condition like that, it was pretty plain that if the airplane went below the glideslope, school would be out. To that end, I remember the simulator instructor telling me that I was over-temping the engine on final. My apologies to Pratt & Whitney because I was going to do whatever was necessary to keep the airplane on the glideslope and if the engine would produce the power, I was going to use it.

It worked. I broke out of the simulated icy clouds and made a hot landing on a long runway. I didn’t start reducing power until I was close to the runway.

I think that icing simulation came from a Caravan accident where so much ice accumulated that the airplane could no longer maintain altitude. That Caravan had boots. The airplanes can now be fitted with TKS (weeping wing) systems and if a Caravan pilot reads this I would be interested in any comparison of the ice ability of the airplane with TKS v. boots.

I flew my P210 for 28 years and close to 9,000 hours. It had a boot system that was approved for flight in icing condition (the word “known” was not in the icing approval) and I never cancelled a trip because of forecast icing. Mainly I would go look and think of the boots as something to use while I was getting the airplane out of any icing condition that was encountered.

A high-wing airplane does have a definite advantage in ice. The accumulation aft of the protected surfaces that is always mentioned is on the bottom of the wings. I could see the bottoms of my wings.

When you are flying in cold clouds it is important that you know a lot more about the meteorological moment than is covered in testing and training but I will leave that subject for another day.

Finally, I told you I would share with you the theoretical recovery from a spiral dive. A Cessna engineer once told me that the only airplane they ever did an intentional spiral dive in was a T-37. (Maybe our Cessna historian, Harry Clements, remembers something about this.)

My information on this came from a Beech engineer. Apparently they had given a lot of thought to the subject because of the high spiral dive involvement of V-tail Bonanzas in years past.

In theory at least, an airplane reaches an equilibrium in a spiral dive. The g-load might be in excess of the limit load factor but not the ultimate load factor. There is no history of airframes failing in the spiral itself, only during an attempted recovery.

With high airspeed, the first recovery step is to level the wings. That would be true in a spiral dive but what happens next is the problem. When the wings are leveled the airplane will then seek the speed for which it was trimmed before control was lost. In a theoretical spiral recovery the g-load would stay the same when the wings are leveled. It would not increase. Theoretically the airplane won’t break itself so once the wings are level the pilot has to not apply any elevator force because that would disturb the natural course of events.

It goes without saying that the zoom would be spectacular but if power were reduced to idle, as it should be, the speed would dissipate rather quickly and normalcy could be regained.

I never tried that because I learned early on that keeping the wings level is a key to everything in aircraft control. A loss of roll control can only lead to ever-worse things.

An icing article in Air Facts many years ago had a fine title: “Ice is not Nice.” Truer words were never spoken. Do you have any icing war stories?

6 Comments

  1. John says:

    I remember this TBM story when it first broke, I recall the pilot’s wife and kids were on board. Horrible, horrible, turns my insides with sadness.

    As for war stories, one winter night while working on my IFR rating, my instructor and I punched into low clouds to shoot local approaches. Flying outbound on the VOR solidly in the clouds, I was scanning the Skyhawk’s instruments and to my amazement watched the airspeed needle slowly and steadily drop from 100 knots to 90, then 80, then 70, then 60, all the way to zero. And I mean zero, needle was pointed straight up. How can this be I asked myself? The engine is purring along and the artificial horizon is steady, vertical speed zero, turn coordinator centered. Pointing it out to my instructor, he replies “Oh, we forgot to turn on pitot heat.” I flipped the switch and pretty soon we had the airspeed indication back. We landed in snow showers that night and I noticed all kinds of ice buildup when I tied the airplane down. The complications of weather flying hit home that night I assure you. True Story.

    God bless that TBM pilot and his family/passengers. For that matter, all of us.

  2. Bones says:

    I had one significant icing encounter in my Mooney C model. Going up was not an option and there wasn’t very much “down” to work with. After a fairly short encounter I was full throttle indicating 80 mph feeling the stall buffet. There was a chunk about 3″ deep on my temperature probe on my side window. The mixed ice on the leading edge formed formed a Y turned 80 degrees to the right….about as unaerodynamic as you can get. Thankfully a broke out into sunshine and the ice sublimated, but it was pretty tense for while.

  3. Duane says:

    Interesting and tragic accident, and very interesting post on the subject of recovering from a spiral dive. Two lessons seem evident:

    1) If the pilot had investigated the weather properly before takeoff, then the logical course would have been to avoid penetrating the cold front in the clouds, which is a natural place to encounter icing in the winter. Knowing how badly this attempt to penetrate turned out, in similar conditions I would seek an IFR routing that kept me in the sunshine, perhaps at a nearby hold, and climb to above the cloud tops, then proceed on course. A TBM700 has a climb performance of something better than 2,000 fpm, so it would only take a few minutes of climb to get to altitude. You give up maybe 8-10 minutes of fuel burn in return for the lives of yourself and your family … that seems like a very good trade.

    2) Regarding your proposed spiral dive recovery, Dick, it makes perfect sense to do what you say. The problem is, it runs counter to a pilot’s natural tendency to pull up on the stick to preserve altitude in an unintended dive. Sort of the opposite of the “big push” necessary during an engine-out shortly after takeoff. All pilots intellectually know that lowering the nose is necessary to maintain airspeed – yet it runs counter to natural tendencies … unless practiced. These kinds of situations illustrate the value of simulator training, because in a simulator we can safely do things that are not very safe to do in a real airplane, yet help to develop non-intuitive habits of emergency response.

    Thanks very much for sharing.

  4. Cary Alburn says:

    In 4 decades, I have had a few icing encounters, which I’d not like to repeat. The first one was while my airplane pard was in the left seat, I was giving him some ad hoc instrument instruction (I wasn’t his regular CFII, but I had just gotten my CFII and he was close to taking his IR checkride, as I recall). Anyhow, we had been flying in between layers from Laramie to Idaho Falls, and as we came down the ILS to KIDA, we went into a layer that was full of moisture. The airplane iced up so fast that it was amazing. I told him to keep the speed up, which he did, and then when I saw him reach for the flap switch, I said to land without flaps. There was a tiny hole clear of ice in the windshield, about an inch on the leading edges of the Skylane’s wings and on the tail. As it got warmer, though, it started to break off in chunks, which hit the tail and made loud bangs. It also caused the wings to have different amounts of lift, so there was a lot of roll moment. When we landed, the airplane still had ice on it, but a lot of it was melting.

    Another one was in a C172RG, Laramie to Jackson. I was at 14,000′ approaching the Dunoir VOR, in apparently clear air, when the wings started collecting rime ice. I called Salt Lake Center and advised them I would need priority treatment, because I was starting to collect ice. The controller said I was number 4 for the approach, but I said that if I didn’t become number 1, it would soon turn into an emergency, because a 172 can’t carry any ice (not true, it can carry a little, but who knows how much?). He held the other airplanes (all twins with deicing), and cleared me for the approach. By the time I was on the ground, all of the ice had melted and the airplane was just wet.

    The worst one was in a Mooney 231, enroute Laramie to Durango at 12,000′ in very cold air, probably -10F, maybe a little warmer. The windows were all frosted over inside, but looking at the wings, they didn’t appear to have any ice on them. We were mostly between layers, although occasionally busted a cloud or two. Just north of Pueblo, it got pretty quiet, and the engine started to wind down. Airspeed dropped off as the autopilot attempted to hold altitude, so I kicked it off, declared an emergency, and asked for vectors to Pueblo. Unfortunately, Pueblo’s weather was only 200′ and half a mile, so it didn’t seem too promising to get in there with a dead engine. Of course, I went through all of the checks to see if I could restart, fuel, mixture, boost pump, etc.–and suddenly remembered that the Mooney had a manual alternate air door operated by a pull knob under the panel, just above my right knee. I pulled it, and the engine came to life. We climbed back up to 12,000′, and I advised ATC that I had the engine back. We flew on to Durango, and when we got on the ground there, there was literally a couple inches of ice covering the front cowl of the airplane, completely blocking the air intake. So that was a different kind of icing, but just as dangerous as icing on the wings.

    Otherwise, I’ve had some minor rime icing on Skylanes at other times, which quickly went away by changing altitudes.

    But the bottom line is that ice of any kind on the wings and tail can materially damage their ability to fly. In olden times, we were told that you could “polish” such ice during preflight and safely fly, but the FAA backed off of that position some years ago and now says that it must be totally removed–and I fully agree. It’s the only way to be safe.

  5. Giuseppe says:

    October departure, Manhattan KS, October at night. This was my second leg of a long day; I’d originated in severe clear Gunnison and flown over Pikes Peak to Manhattan. My second leg route of flight was to skirt the back side of a cold front (and line of TS), turn right up south of Des Moines, and proceed east to Fort Wayne. I was flying my turbo-Viking. I was concerned about fuel and had flight-planned a route that appeared to give me roughly 25 miles clearance around some bad storms as I proceeded northeast. ATC was matter-of-fact and helpful as I departed Manhattan.

    I was on the autopilot, trimmed up and leaned out, in the climb and IMC, in absolute darkness. Leaving about 8000, as I was settling in for the flight, I bent over to fiddle with my CD player, which was refusing to eject a disc. Then things sounded different.

    I looked up. My airspeed was unwinding, seemingly at the rate of a second hand sweeping counterclockwise. I pulled my flashlight and check out wing icing. All of the glass was solid, opaque. This had happened within 10 seconds. I went full-power/full-rich, requested an immediate climb, which I received. Aircraft continued, evidently, to slow.

    Some now will suspect that I had two problems, and had to decide which one to address first.

    I called ATC back, and I recall my exact words: “This isn’t working. Request lower.” Guy said, “Anything you want.”

    So, back to my two problems. I chose to address the failed pitot heat, because my IAS was so dropping through 90 while my GPS groundspeed showed significantly higher. I bet the flight on GPS groundspeed, abandoned IAS, pushed the nose down, and shed the ice a few minutes later.

    This was a very unpleasant experience. There was no gradual accumulation of ice; it was as though the plane had been dunked in the stuff. I could not verify the condition of my wings, and according to my airspeed indicator I had 20 seconds of declining airspeed prior to stalling. I fly a lot across the Appalachians, and through the Great Lakes region, but the routine light icing moments there were nothing like this event.

    I also do a better job of pre-flighting my plane these days.

  6. John Swallow says:

    Dick: Many years ago, the RCAF Air Navigator School in Winnipeg was using the DC-3 workhorse as their training platform. An apochryphal story from that era is that three of them were on the ground on a miserable winter day in Thunderbay, ON after refueling awaiting their turn to get airborne further eastbound. Their departure was held up due to an incoming C-45, another RCAF aircraft, inbound from Trenton, ON. As they three “Daks” waited on the taxiway at the end of the runway, an ice-covered C-45 emerged out of the low clouds and executed what can best be described as an “undignified arrival”.* One by one, the three Winnipeg-based Daks cancelled their IFR flight plans and trundled back to the ramp.

    Sometimes discretion IS the better part of valour…

    *Later discussion with the C-45 crew revealed that near full power was required in the latter stages of the approach.