Flight Safety: Combined Experience and Training Allowed KC-135 Crew to Work Through In-Flight Issues and Land Safely

By MAJ TAYLOR ZAHM, 22D EXPEDITIONARY AIR REFUELING SQUADRON

On March 4, 2020, my crew and I arrived at our KC-135R, an aerial refueling tanker, at Incirlik Air Base in Turkey. As the aircraft commander I was on my seventh deployment and was an instructor/evaluator, the copilot was on his third deployment, and the boom operator was on his first. We checked the aircraft forms, performed applicable checklists, and took off with zero issues—a good day! For most of our sorties we delivered approximately 150,000 pounds of fuel to our receivers and then flew back home with fuel to spare. Some aircraft can carry 300,000 pounds of fuel and some can carry only 10,000, but for the KC-135 that was a fairly heavy load. A fuel panel for the 10 tanks on the aircraft manages their center of gravity, defines where the engines are burning fuel and from where it is being offloaded, and the equality of the wing tanks. The crew can also move some of the fuel around using this panel.

We reached our assigned altitude and began routine level-off checks— hydraulic and oxygen quantities and pressures, electrical and engine systems, and moving or burning fuel from different tanks. Proceeding to a predesignated waypoint, I started a drain from two of the main wing tanks to prepare for our upcoming refueling. I pressed the drain button for the number 4 right wing tank to move fuel to the aft body tank so we could offload that fuel to our receivers. The button indicator light went from “closed” to “open,” and the fuel started decreasing in that tank and increasing in the aft body tank. I then pressed the drain button for the number 1 tank to do the same, but nothing happened. Confused, I pressed the button again with the same result. Finally, I slowly pressed the button to ensure it went from “closed” to “drain.” The button proceeded about a quarter of an inch past the point where it was supposed to stop, and then all the light indications vanished. I grabbed the button with my fingers and brought it back out to where it should normally rest, and it lit up again in the “closed” position. I then stopped the fuel drain from the number 4 tank, which had still been draining, but only for about 45 seconds, and there was not a significant difference in fuel values yet.

I tried again to drain fuel from the number 1 tank, but the button stopped about a half inch beyond where it should have. The fuel panel indicators blinked, vanished, reset, and then returned. We were about 30 minutes into our flight, and I realized that the total fuel quantity had not moved since the button became stuck. I checked the tank quantity reading on one of the Control and Display Units (CDU) and saw that none of the fuel panel indicators were correct.

The main fuel tank, primarily for feeding fuel into the number 1 engine, was stuck in the draining position, a fuel imbalance had developed between the left and right wing, and a fuel panel was showing us incorrect readings. We were traveling approximately 6.5 miles per minute on an airplane that weighs about 270,000 pounds. So we did what every system simulator, table­top emergency procedure quiz, and years of experience had taught us— we let our training take over.

We started draining the working number 4 tank so the airplane could fly straight. The boom operator checked the flight manual for any emergency procedure we could reference. The copilot grabbed a multi-tool to try to pry the button back up while I flew the aircraft, and I made a quick radio call back to our deployed unit. I could not reach the operations center, but I reached another KC-135 that was 20 minutes behind us, and they also checked the flight manual to see what we could do. The copilot took the aircraft back and flew as steadily as he could. I compared the frozen fuel panel to the CDU—the fuel panel was still lying to us and the CDU was showing the number 1 and number 4 tanks draining past 7,000 pounds (we started at 14,000 pounds). Then the other KC-135 called back and referenced an emergency checklist that discussed a fuel panel button becoming stuck in the closed position, advising that we “land as soon as possible.”

The fuel panel and the CDU told us we were still draining fuel. I suggested we fill the aft body tank to prevent the number 1 tank from draining beyond a point where we could not keep enough fuel in the tank for the engine to burn. The copilot announced the maximum amount the aft body tank could be filled to, and we decided to open all the tanks from the wings to drain aft into that tank. This procedure would hopefully fill up the aft body tank faster than it could deplete the number 1 tank. After a few tense minutes of watching the number 1 tank trickle down to 1,800 pounds, it stopped! The wing tanks on the KC-135 are designed so you can only drain down to approximately 300 gallons (about 2,000 pounds of fuel), and the aft body tank could only fill up to around 42,700 pounds. When the drain from number 1 stopped, the aft body tank was reading 42,700 pounds. Now we needed to keep positive fuel pressure into tank number 1 from that same aft body tank to make sure the engine did not burn the rest of the 1,800 pounds it had left. We did not have long if we could not keep fuel from the other tanks feeding the number 1 engine.

We had stopped the drain from our number 1 tank, filled the aft body tank, kept our center of gravity in a good landing position, and maintained fuel balance between each wing. We had left the fuel in the reserve tanks. Approaching home, we were able to contact our operations center. We proceeded to an established gross weight adjustment zone to offload fuel to a level that would not overstress the landing gear upon return. This zone was close to our deployed home station, so we would already be on the radio with the controller to be vectored for a short approach and landing.

The boom operator prepared for the fuel dumping, but with the faulty fuel panel, which pumps worked? Which drains worked? Which manifold valves worked? Could we even adjust gross weight? We decided that we did not have time to find out. We declared an emergency to ensure that we were placed on a priority status. We informed our home station air traffic controller that we would need a vector for home in roughly five minutes. We discussed the eccentric details of landing a KC-135 this heavy— approach speeds, landing distances, fuel panel configuration, landing techniques, how quickly we would need to brake to stop our momentum, and how hot the brakes would get. We tried to cover every scenario. All we did know was that we did not want to be the guinea pigs for a new emergency checklist!

Our brief descent was met with calm winds, high visibility, and a very stable aircraft due to it being so heavy. We made our approach and stopped well within the total landing distance the Take Off and Landing Data (TOLD) had provided us. We pulled clear of the runway and called for the fire trucks to check for structural damage, leaking fuel, or brakes that were on fire. The landing gear started to produce smoke, and the on-scene fire chief directed a crew evacuation. We ran the applicable checklists, grabbed our personal and mission bags, and drove to maintenance to give them the bad news.

If I were to change anything about this incident, it would be to design an emergency checklist to address this situation. The actions we took got us home, but were they the correct ones? We kept the engines running, used snippets from other checklists, applied common aircraft systems knowledge, and called on anyone with experience to help. I am eager to learn if there was something we could have done differently to be more effective.

The other thing I would change is to reiterate clearly that the main wing tanks will drain to approximately 300 gallons, and the rest will remain for airplane use. I could only find that information after searching three different technical documents, and even that was buried within a system diagram note. I suggest putting that information in a new checklist or within the fuel emergency checklist I referenced most during the event.

The best thing about an aircraft like the KC-135 is the crew. I credit our successful recovery of an undamaged KC-135 (other than the fuel panel and the brakes) to our ability to combine our experience and training and apply it to a situation that does not have any emergency checklists to reference. It could have ended much worse—the engine could have flamed out, we could have had wings that were 14,000 pounds different in weight, or we could have snapped the landing gear. Thankfully, none of that happened. I guess that is because we train so hard for these situations. Everything else falls away and you are left with your training and your crew.