USAF Cessna T-37B (photo from “Cessna Warbirds” 1st edition)
My first assignment after earning my Air Force wings in August 1970 was to stay on at Webb AFB (Big Spring, TX) as an instructor pilot in the primary jet trainer, the Cessna T-37 Tweet. It was not the assignment I wanted, but Mother ATC (Air Training Command), in her infinite wisdom, decided that was where I could best be used.
Webb AFB closed in 1977.
I then spent four months at Perrin AFB (Sherman-Denison, TX) for T-37 Pilot Instructor Training and returned to Webb to start training student pilots in January 1971.
Perrin AFB closed later in 1971. (Sounds like a trend. My first two bases closed soon after I left… But I tried to make up for it by helping re-open a closed base in 1973.)
We always knew the Tweet, with its big fat wing (typical of all Cessnas of the era) would take a lot of ice buildup and keep on cruising along, although flying it in known icing conditions was a no-no (it had no de-icing equipment). On February 10, 1972, I had a personal demonstration of just how much ice you could have on a Tweet and still fly safely.
On that date, my flight commander Maj. Officer (that was really his name) and I departed Webb AFB on a planned proficiency sortie down to San Angelo and back. Weather at Webb on departure was less than great and not much above approach minimums. The forecast, however, indicated a slow improvement.
So much for forecasts.
As we climbed out of San Angelo following a radar approach, intending to head for home, Center informed us that Webb had just dropped below minimums, as had Dyess AFB (Abilene). Oh, and the runway at San Angelo was closed.
They wanted to know our intentions. As if we had many choices.
You see, the T-37 had one significant problem for cross-country purposes. It didn’t carry much fuel. Typical sorties lasted about 1.3 hours, and a flight of 400 nm was pushing the limits for going anywhere.
We asked for clearance to higher altitude immediately and direct from our present position to Randolph AFB (San Antonio). That would result in stretching our fuel, but San Antone was warmer with only mid-level clouds. We got our requested clearance and headed south.
As we leveled off at FL230, still solidly in the clouds, we noticed ice starting to build up on the leading edge of the wings, as well as on the engine inlet lips. The highest we could legally fly (in our unpressurized cockipt) was FL 250 and that was not available (and wouldn’t have made much difference anyway). If we descended to lower altitudes, where the air was warmer, we wouldn’t make it to Randolph.
Maj. Officer assured me that there was no cause for concern since the T-37 icing was not much of a problem and it could handle a lot of ice. I accepted his assurance as he had a lot more experience in the little jet than I did.
Then the left engine flamed out. I looked out and saw that the ice on the inlet lip was gone. It had apparently broken off, was ingested in the engine, and caused the flameout. The engine restarted easily, but ice soon began building up on that inlet again.
A few minutes later, the right engine flamed out. Same cause, and it also restarted easily.
As we neared San Antone, we were informed that Randolph AFB was now PPR (Prior Permission Required) for some unknown reason. We elected to divert to Kelly AFB on the SW side of San Antone. Meanwhile, the left engine flamed out again and again restarted.
T-37 icing might not be much of a problem for the airframe but wasn’t very good for those old cast iron, turbojet engines.
Ice on the wing’s leading edge looked to be very thick, and we estimated it at close to 2″. That’s a lot of ice and was certainly going to affect the little jet’s handling and stall speed.
We requested, and received clearance for, a straight-in descent to radar final at Kelly. As we dropped into warmer air, the leading edge ice began dissipating, albeit very slowly.
As we let down to Kelly, we discussed how much to adjust our final approach and touchdown speeds for the unknown effects of all that ice. We finally, somewhat arbitrarily, settled on an extra 20 knots down final and planning a touchdown at not much less than that. After all, Kelly has a runway about 3-4 times longer than a Tweet would need under normal conditions, and there was no reason to suspect that the brakes wouldn’t work normally.
So, we flew down final at 120-125 KIAS with Maj. Officer at the controls. The aircraft seemed to behave fine. Officer touched down in a flat attitude, no reason to flare out and find out where the stall speed was with all that ice, and let it coast until almost to the last turnoff.
We taxied back to the transient ramp, a long taxi in 40-45° temperatures and the Fuel Low Level light glaring steadily at us. After climbing out of the aircraft, I chipped off a piece of ice from the wing’s leading edge.
It was a good 1″ thick, despite the taxi back in the relatively warm air. That’s a lot of ice. I wish I had had a camera to take a picture of it.
The transient maintenance crew inspected the engines later that day and found them fully operational. The ice ingestion had done nothing but put out the fire as it melted.
So, T-37 icing might not have been a big problem, but it was certainly something to be avoided. After all, those flameouts could have occurred on final approach at a much slower airspeed, maybe even an airspeed below the iced-up stalling speed.
Just one more lesson learned and filed away for future reference.