At night, while most of us sleep, hundreds of airplanes crisscross the starry sky. FedEx, UPS and many smaller carriers operate a shadow airline system, a transportation network built for boxes instead of people. It’s a remarkably reliable system. But on Dec. 9, 2019, a series of ignored red flags led to the fatal crash of a Cessna 208B Super Cargomaster Caravan.
A little before 8 p.m. on a dark Texas night, the experienced airline transport pilot (ATP) got ready to conduct a regular UPS feeder flight. The plane was one of 29 Caravans flown by a Part 135 cargo operator. Cessna 208s are beefy single-engine unpressurized turboprops, with fixed gear and wing struts—they look like pumped-up versions of a 172. In addition to cargo hauling, they also find worldwide use in skydiving and passenger flying jobs.
This intra-Texas flight was to go from Victoria Regional Airport (KVCT), a small tower-controlled airport in South Texas, to Houston’s George Bush Intercontinental Airport (KIAH) using the callsign Martinaire 679. It was easy weather for Instrument Flight Rules (IFR) flying. Winds were light, visibility 6 miles in haze, a few clouds at 2,800 feet and an overcast layer starting at 4,700 feet. No precipitation in the area. A routine run.
Victoria Tower air traffic controllers (ATC) were the first to notice the pilot had problems. Martinaire 679 was cleared to taxi to runway 13L but made some wrong turns. “You are going the wrong way, make a one eighty and taxi alpha to runway 13L,” said the ground controller. The pilot found the runway and, at 8:02, was cleared for takeoff. Victoria Tower handed him off to Houston Center at 8:04, informing the radar controller on the landline that the big Cessna was, “coming to you, he is a winner.”
“Victoria Tower handed him off to Houston Center at 8:04, informing the radar controller on the landline that the big Cessna was, ‘coming to you, he is a winner.’”
Radio transmissions with Houston Center started normally but soon turned worrying. ATC instructed Martinaire 679 to maintain 3,000 feet. The pilot read back the clearance. A minute later, ATC asked the pilot to say heading. The reply was unintelligible. The flight was then cleared direct to waypoint GMANN. The pilot correctly read back that instruction. Another minute later, Houston said, “I’m showing you heading southeast bound.” The reply was indecipherable. Houston then issued, “fly heading 035 degrees,“ which the pilot read back. However, the radar display wasn’t showing a consistent track to the northeast, so the controller told the pilot to advise when he was on a 035-degree heading. Observing the airplane still turning, Houston Center then reiterated the instruction to fly heading 035. The replies were indecipherable.
At 8:11, Houston transmitted, “I’m showing you like going back left, right, left and right, what are you showing on your heading?” The pilot replied, “I’m heading, um, ah, three six zero. I am correcting; I have some instrument problems.” The controller asked the pilot if he needed to go back to Victoria. The pilot advised he would continue to George Bush Intercontinental. Then, at 8:12, the pilot transmitted, “I go back to Victoria.” ATC cleared him direct to the airport, advising it was at his 12 o’clock position and 6 miles. The pilot said he was looking for the field but never reported seeing the airport. Or maybe he did; we can’t really say for sure as all his transmissions were now unintelligible. ATC started issuing vectors for an instrument approach.
The FAA controllers were clearly concerned for this pilot. Their radar/ADS-B displays showed a target moving erratically, with multiple reversing turns. A more experienced controller, who was also an instrument pilot, took over the position and issued several repeated instructions. He planned to speak in plain English, establish straight and level flight, then issue no-gyro instructions to the airport. But there were no replies to his transmissions. Houston Center called Victoria Tower and asked if they had the Caravan in sight: “I don’t see him, there’s a lot of haze and clouds rolling in.”
Radar contact was lost when the plane suddenly descended in a power-on, near-vertical dive to the ground. The prop buried itself 5 feet down into the clay soil. The pilot died instantly of blunt force injuries.
After the accident, the National Transportation Safety Board (NTSB) was faced with a fatal Part 135 air carrier accident with no eyewitnesses, no video recordings and no survivors. What was left of the plane was highly fragmented after the high-energy crash into terrain. FAA regulations for these commercial operators don’t require cockpit voice recorders (CVR) or flight data recorders (FDR). That they were able to uncover the cause of the accident is a testament to old-school crash investigation detective work. And the power of X-rays.
The Safety Board found the pilot was having a hard time holding headings because his Attitude Indicator (AI) and Horizontal Situation Indicator (HSI, a type of heading indicator) weren’t working. Control in the clouds is nearly impossible without an artificial horizon and directional gyro.
In the accident plane, both these gyroscopic instruments were electric units, and they weren’t working because neither of the two possible sources of power (an electrical system component called an inverter) was supplying power. Only two of the airline’s fleet of Caravans had inverter-powered instruments, but the requirement on these planes to switch on an inverter was covered in training and in their manuals. The airplane’s engine start checklist required an inverter be selected on. The taxi checklist required an inverter be checked on. And the before-takeoff checklist required the annunciator panel to be checked to indicate that no warning lights were illuminated.
Maybe both inverters had failed. Or maybe an inverter broke in flight, and the other one wasn’t then switched on. Or possibly neither one was ever switched on. We’ll never know because both inverters and their associated switching panel were completely destroyed in the crash. So how did the NTSB establish that these instruments weren’t powered?
The 208 has a large annunciator display above the attitude indicator, at the top of the instrument panel. It’s a rectangle of 8-by-3 boxes that light up to show the status of various systems. If oil pressure is low or a door open or a similar anomaly, then two incandescent bulbs light up a color-coded label. The annunciator display had survived the crash mostly intact. Using X-ray imaging, the NTSB Materials Laboratory examined the filaments inside all the light bulbs. A couple had broken in the crash. Most, however, were intact and appeared identical. Except for two. The filaments of the two bulbs in the INVERTER INOP indicator had been stretched. Which is exactly what happens to a light bulb subjected to sudden deceleration while it is lit, when the little piece of glowing metal is hot and somewhat pliable.
The INVERTER INOP annunciator wouldn’t have been the only indication of unpowered primary instruments. Each gyro instrument has red warning “flags” that appear when it’s unpowered or at low gyro rotation speeds. You see them climbing into an unpowered cockpit. The NTSB closely examined the internal parts of the gyroscopes in the AI and HSI, and found no rotational scoring that would have been present if they had been spinning at the time of the crash. Like most turbine Cessnas, the 208 has a second set of instruments on the right, or co-pilot, side of the cockpit. These are vacuum powered, and those gyros did show rotational scoring. Now, the NTSB had proven that neither inverter was powering the pilot-side instruments and had shown the primary gyro instruments were not operative while the set on the right side worked.
The Safety Board determined the probable cause of the crash was “the pilot’s loss of control due to spatial disorientation. Contributing to the accident were the inoperative attitude indicator and horizontal situation indicator on the pilot’s side of the cockpit.” The board also correctly cites his failure to use the flight instruments on the co-pilot side that were still working. And, going further, it found the red flags on the instruments weren’t the only warning signs that may have been ignored. The pilot had a checkered history.
The 61-year-old had an estimated 12,600 hours of total flight time, including 1,300 hours in Cessna 208s. He was hired by the cargo carrier in November 2017, and his training record shows slow progress. There are handwritten notes like “scanning poor…basic maneuver skills need work…poor listening skills to ATC…situationally unaware…cross checking + scan needs work.”
The chief pilot told the NTSB he was a “slow learner” but was also “conscientious and difficult to upset.” He added that the pilot’s “preparation was usually acceptable, and he was comfortable flying with him.” Less positively, the chief pilot recalled that the pilot’s last check ride was in an inverter-equipped 208, and he “required instruction on the use and function of the inverters, including the requirement to select one of the two inverters during the engine start checklist.”
“It’s easy to say the pilot should have seen the red flags on the instruments. It’s easy to say he should have turned on an inverter, considering the INVERTER INOP annunciator was brightly lit right in his face.”
On Jan. 1, 2018, the pilot struck a taxiway sign while exiting the runway and received remedial ground training. Then, in September that year, he chose to leave the cargo company to work for a passenger-carrying Part 135 operator in Hawaii. It flew Cessna 208 Caravans, so it should have been an easy transition. He didn’t last long. The director of operations at the Hawaiian air carrier told investigators the pilot “had issues beginning in ground school; he didn’t know limitations and the language barrier was a factor in his learning ability. Once he was in [simulator training], we noticed instrument skills and maneuvers below standards and choose to discontinue his training.” The pilot returned to Texas. The cargo company hired him back, knowing he’d (in the words of the chief pilot) “washed out” of training in Hawaii.
It’s easy to say the pilot should have seen the red flags on the instruments. It’s easy to say he should have turned on an inverter, considering the INVERTER INOP annunciator was brightly lit right in his face. It’s possible to imagine flying back to Victoria using the working right-seat instruments. Instead, he lost control and crashed.
It’s harder to say what to do when seeing red flags in a pilot’s performance. Those warning signs aren’t always so distinct. I know from experience it feels horrible to deny pilots good flying jobs. But the passenger operator in Hawaii made the tough call. And maybe that’s why it was boxes, not people, in the back of the plane on that hazy night.
Want more After the Accident articles? Read “Taking Off With Controls Locked Proves Fatal For Pilot.”