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Volume 26, Number 14e
April 5, 2019
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Investigators Fault MCAS In Ethiopian Crash
Paul Bertorelli

Boeing’s MCAS stall-protection system was at fault in the crash of an Ethiopian Airlines Boeing 737 MAX 8 on March 10, according to a preliminary report released early Thursday. An earlier report showed that the aircraft’s flight data recorder revealed that the crew initially followed procedures Boeing recommended to disable the system, but then inexplicably re-enabled it.

The Wall Street Journal reported that investigators led by Ethiopian authorities believe that MCAS—which may have been erroneously activated by a faulty angle-of-attack sensor—caused uncommanded nose-down trim which the pilots were unable to effectively counter. The FDR readout showed that the crew initially followed Boeing's recommendation to use the 737’s stabilizer trim cutout switches to disable MCAS and revert to manual trim. But the data also showed the pilots re-engaged electric stabilizer trim, thus re-enabling MCAS, a background stall-protection system that automatically rolls in nose-down trim when the airplane is hand flown at high angles of attack with the flaps retracted. But it relies on the airplane's electric trim system to command trim.

Boeing is developing new software for the MCAS system, but it’s weeks if not months away from approval. Meanwhile, some 370 MAX series airplanes remain grounded throughout the world. Boeing CEO Dennis Muilenburg said Wednesday that he had joined Boeing test pilots for a demonstration of the revised MCAS software and that the company would “take the time to get it right.”

MAX And The Press
Paul Bertorelli

If Boeing wanted bad press for itself, it couldn’t have done any better than the unfolding drama of two hull losses of the 737 MAX 8 within five months and the slow drip of daily coverage on what crash investigators are learning. Overall, I give the daily press a B+ for its coverage. It has generally been fair, accurate and technically competent.

But as I write this, there’s a story circulating in print and broadcast that appears to be flat out wrong in the detail that’s important to this kind of coverage. In fact, reader Don Dillman emailed me to say that we—well, me—got the headline wrong on a recent story. It said that the Ethiopian Airlines pilots followed Boeing’s recommendations on disabling the MCAS after experiencing uncommanded trim. But that’s not correct. They initiallyfollowed Boeing guidelines by using the stab trim cutout switches, but then—inexplicably—re-engaged electric trim, and thus the MCAS stall protection subsystem that appeared to be causing the runaway trim in the first place.

I explained this correctly in the story, but I couldn’t make it fit in the headline. I went back into the story and tweaked it. We can do that in online publishing. In newspapers, it awaited the second edition or the next day’s fish wrapper. But broadcast outlets, including NPR, are still getting it wrong, without the nuance of the pilots using the cutouts and then re-engaging them for reasons we can’t, at this point, grasp.

Just to review, by requirement of AD, following the Lion Air MAX crash in Indonesia in October, Boeing sent out a detailed bulletin explaining how to handle an MCAS abnormal, including what indications pilots should expect to see. These included continuous or intermittent stick shaker on the affected side only, an airspeed and or altitude disagree warning, a minimum speed bar and increasing nose-down stick force.

The response is typical of a runaway trim condition. Boeing said to disengage the autopilot and use electric trim as required. If relaxing the control column causes the trim to move, set the electric trim cutout switches to disable the trim. If the trim still moves—I’m not sure how it could—then the pilots can hold the trim wheels and trim by hand. As we’ve reported, the 737 MAX 8 is a bit of a throwback, in that it has large trim wheels on either side of the pedestal between the pilots. It can be manually trimmed, albeit somewhat laboriously. Either way, Boeing said to leave the stab trim switches in cutout for the remainder of the flight.

If The Wall Street Journal’s reporting on the FDR output is correct, the Ethiopian pilots first followed the procedure by using the trim cutouts. But then they re-engaged the electric trim, allowing the ostensibly malfunctioning MCAS subsystem to get at the stab trim and start cranking the nose down again. But this is not what Boeing recommended, ergo, they didn’t follow the procedure.

This is an important detail because ignoring it suggests that there’s something seriously amiss that isolating the electric trim can’t correct. It’s not impossible that this is the case, but there’s no evidence to suggest that it is. As journalists, we owe it to our readers to get this as right as possible. Including the headlines.

Note to Readers: No, it's not something you said. Because of persistent denial of service attacks against AVweb, we're moving the site to another platform. The commenting section will be unavailable for a time. We apologize for the inconvenience, but the site will be better for it in a week or two. In the meantime, if you have a comment, email us and we'll append it to the blog.

From one armchair accident investigator to another…

I just finished reading the Preliminary Report from the Ethiopian AIB. I have come to the astonishing conclusion that one or both of the flight crew did not understand once the stab trim cutout switches are in cutout, you MUST use the manual trim wheel to adjust the stabilizer trim. At 41:50, the First Officer should be cranking away on the manual trim wheel and not fussing with the electric trim switches on the yoke. If you zoom in and study the chart on page 26, you will find that at no time during the flight was the stabilizer trim adjusted using the manual trim wheel.

Contributing Factors: I suspect there is confusion about the meaning of the term “Use Manual Trim”. Boeing thinks it means use the manual trim wheel. The First Officer seems to have thought it means use the trim thumb switches on the yoke. When the trim switches didn’t work, someone turned the electric trim system back on in a last ditch effort to regain trim control. Unfortunately, that let the MCAS devil back into the cockpit. Also, the final paragraph of the Runaway Trim procedure can lead one to believe the using electric trim to correct an unexplained out-of-trim condition is an acceptable procedure. Paragraph 3 says leave it in cutout for the remainder of the flight, but the final paragraph tends to conflict. It would probably be best if Boeing deleted that final paragraph.

Jeff Moffatt

Your post says “Boeing said to disengage the autopilot and use electric trim as required.”So what wasn’t clear to me was:

  1. Why is the pilots’ decision to use electric trim “inexplicable”
  2. We have been told that MCAS is only active with the autopilot off, so why “disengage the autopilot”

Take it for what it’s worth – I’m sure you’re getting tons of half-baked armchair feedback.

Aarohi Vijh

Most of the mail we're getting is fully baked, as are your questions. As noted in today's story, the pilots already had disagree alerts and stick shaker on one side before engaging the autopilot. I'm told by pilots consulting with us that enaging the autopilot at that stage is not good practice.

Your reporting is usually very objective, to the point and factual. But I have to take issue with many of the strong definitive-sounding statements you make in today’s article about the 737 MAX.

Title: "Investigators Fault MCAS In Ethiopian Crash”. Absolutely not. For starters, the entire preliminary report by the ECAA does not mention MCAS at all. Search for it. You will not find MCAS anywhere in that report. They refer to automatic aircraft nose down trim, but not MCAS. Presumably the AND could be caused by MCAS or some other subsystem. Yet to be determined. So no, they did not fault MCAS. They do not even mention MCAS. Even the Minister was asked repeatedly about MCAS at the press conference, and never ever blamed MCAS, only said that the pilots were unable to override the system. Further, this is a preliminary report. The investigators do not identify causes, nor contributing factors. They are not assigning blame. Not yet. Your title is way too sensationalist and not at all reflective of what the investigators have said.

Then, in your article you say that "the data also showed the pilots re-engaged electric stabilizer trim” and that “they […] inexplicably re-engaged electric trim” and that "pilots using the cutouts and then re-engaging them for reasons we can’t, at this point, grasp". No, the data does not show that. Not the data is in the prelim report, anyway. It shows that manual electric trim again became operative, which suggests that the circuit was reestablished. It does not say that the pilots took any action to reestablish that circuit. You could write that you surmise that the pilots may have re-enabled the system, but you should not say definitively that the pilots did, nor should you claim that the data shows that they did. Because it doesn’t.

Then you claim that "the pilots can hold the trim wheels and trim by hand”. Perhaps. Theoretically. At the gate. Notice here that these guys carried a great deal of speed and the aircraft was very out of trim, causing great aerodynamic forces on the out-of-trim tail section. It is quite possible that a pilot would not have the physical strength to turn the wheel by hand. It is also possible that neither pilot had any free hands to go crank that wheel, because both were pulling on the columns just to keep the nose up. Notice that the report states "At 05:40:44, the Captain called out three times “Pull-up” and the First-Officer acknowledged”. "At 05:41:30, the Captain requested the First-Officer to pitch up with him and the First-Officer acknowledged.” "At 05:43:04, the Captain asked the First Officer to pitch up together and said that pitch is not enough.” This to me indicates that the captain (pilot flying) was not able to exert enough force and requested help from the second column. Also from the report "The data indicates that aft force was applied to both columns simultaneously several times throughout the remainder of the recording”. So there. Is it quite possible that the guys were exerting all their force on the columns to keep it flying and had no free hand to crank the trim wheels. “The pilots can hold the trim wheels and trim by hand” is all nice and good at the gate, but perhaps not here. Further, if they really need to trim up and had no hands to turn the trim wheels, it is quite possible that, as a last resort, they would reenable electric trim so that could trim up electrically. This goes back to our previous paragraph and perhaps explain why they may have re-engaged the electric trim, those famous "reasons we can’t, at this point, grasp”.

Let me quote a famous certain Paul Bertorelli: "As journalists, we owe it to our readers to get this as right as possible. Including the headlines.” Please do. Thanks.

Paulo Santos

We'll have to agree to disagree. The preliminary report clearly says the pilots re-engaged electric trim to moved the trim nose-up from 2.1 to 2.3 units.

--Paul Bertorelli

Another facet of this preliminary report that the media is missing – and I don’t fault most them as they are often not aviation experts nor qualified B737 pilots – is that from the moment the aircraft lifted off it had an unreliable airspeed emergency. Disparity between the Captain and FO airspeed indicators, the stall warning (stick shaker), etc. The crew of that Ethoipean flight did not do the recall (memory drill) for that emergency which would later come back to haunt them.
The first thing you do is set the attitude appropriate for the phase of flight (in this case 10 degrees on the attitude indicator) and an appropriate power setting (for the Max I think it is 85%). They did not do this and as we will see later, with the thrust at 100% the aircraft goes really, really fast and is nay impossible to trim.
The other questionable action is not leaving the aircraft in the same configuration (flaps extended) and return to Addis Abba (a maintenance base) to get the unreliable airspeed fixed. Why one would want to continue on a 1 hour flight in stick shaker is beyond me.
Nevertheless, the flaps were selected up and the MCAS failure appeared (which might have been associated with the unreliable airspeed). As the preliminary report states, the airspeed reached between 305 and 340 kts on the RH airspeed indicator and 20-25 kts more on the LH airspeed indicator; meanwhile the engines are at 100% N1 thrust.
As any aviator would know, trim forces increase with airspeed at roughly the square of the velocity; twice the airspeed, four times the aerodymanic force, all things being equal.
Rather than flying the aircraft which includes managing the speed, the aircraft was racing around at Vmo (velocity max operating) with the overspeed clacker going. In addition to not dealing with the thrust right after take-off and the unreliable airspeed indication and setting 85%, 100% N1 caused the speed to increase, making manual trim difficult if not impossible.
As a general observation, I think the media will have to be on the lookout for national bias in this accident as well as the Lion Air one too. Both accidents point directly at professional pilots not being able to handle irregularities that should be easily handled.
Ed McDonald
From a 14,000 hour pilot with 10,000 hours in B737 here. I commend you for your last article and would agree with Ed MacDonald's post. On the Lion Air accident, we can give the crew some slack for dealing with an unknown fault at the time which affected several aircraft systems.
However, in the Ethiopian accident, the crew had all the symptoms of an MCAS failure but did not apply the recommended procedure by Boeing. First the crew wasted precious time trying to engage the autopilot, while the checklist calls to disengage it. Retracting the flaps was also a big, big mistake, which enabled MCAS logic to kick in. If you have stick shaker and IAS disagree alerts, leave the flaps at 5 and come back to land and go have a beer later.
The checklist calls for the Stab Trim Cut Out switches to be left in the OFF position for the REMAINDER OF THE FLIGHT, to Trim the aircraft manually and "ANTICIPATE TRIM REQUIREMENTS. " This is a key statement here. The crew never touched the throttles which were left at takeoff thrust (94.1% N!) allowing the aircraft (which was now level and sometimes descending) to accelerate beyond VMO, making manual trim very difficult if not impossible, due to high aerodynamic forces.
Also, Boeing is skeptical at the possibility of an Ethiopian biased report as they try to protect themselves. A complete FDR and CVR superimposed transcript will reveal exactly what was said and done at specific times in that cockpit. At this time, from the released FDR transcript (CVR was not released) we can only suspect that in a last act of desperation, one of the pilots re-engaged the Stab Trim Cut Out Switches which doomed the flight.

Eduardo Letti

Great work on Max articles. Aviation and investigations can be harsh on pilots. Here are just two examples of "scary as shit" moments where pilots were judged harshly. In the second one, fatally. Perhaps it helps inform the Max conundrum.


Bill Tuccio

I read carefully your report on cockpit activities during the Ethiopian MAX crash and conclude mostly that Boeing does not have a clue what is going on with the aircraft. I think the cg was far enough aft of the neutral point to make the aircraft violently unstable in both the pitch-up and pitch-down senses. Initially the pilot tried to fight the divergences with porpoising, but in the end the pitch-down moments on the fuselage, wings, engine cowls, and tail were too great to be much affected by the pilot's efforts to counteract them with either stabilizer or elevator.

Boeing engineers can and should replicate the event by sliding a paper clip back and forth along a paper airplane. Based on my experience teaching aerodynamics at UCLA and UA up to 1998, I doubt they have the mathematical acumen to understand the fundamentals.
Steve Crow

Vashon Delivers 12 Rangers
Russ Niles

Vashon Aircraft has delivered 12 of its Ranger Light Sport training aircraft and CEO and founder John Torode said the planes have gone to a mix of customers, many of whom will use it as a personal aircraft. Torode, who also founded Dynon Avionics, said that while the aircraft has had some traction as a sturdy and affordable trainer, it has also found a following as a weekend warrior mount and they’re building on that part of the market. A float version will be unveiled in June.

Torode told AVweb that Vashon exploited modern manufacturing techniques and the matched hole process used by some kit manufacturers to squeeze a lot of efficiency out of the build process. They used the familiar Continental 0-200 engine for power and beefed up the landing gear for training in a package that starts at $99,000 ready to fly. He said most customers so far have added optional features, including a two-screen Dynon panel, to build a comfortable weekend aircraft. “You can put a bicycle in the back and just go,” he said. Torode said he’s investigating new powerplants for the plane as its missions evolve.

Video: That's All Brother At Sun 'n Fun
Kate O'Connor

The historic C-47 "That's All Brother" stopped in at Sun 'n Fun 2019 before heading overseas this summer as part of the D-Day Squadron, the American contingent participating in the Daks Over Normandy flyover which will be crossing the English Channel to commemorate the 75th anniversary of D-Day on June 6, 2019. Pilot and member of the Commemorative Air Force Tom Travis discussed the significance of the aircraft, its recovery and restoration, and the reasons behind maintaining warbirds with AVweb at the show.

Podcast: Superior's Scott Hayes Explains The XP-400 and XP-382 Recall
Marc Cook

Last month, Superior Air Parts grounded the experimental-class XP-400 and XP-382 engines after a pair of crankshaft failures believed to be caused by detonation in these engines. Superior then undertook the process of buying these engines back from homebuilders and paying for return shipping. In this podcast, Scott Hayes, Superior's VP of sales and marketing, brings us up to speed on the return process and goes into some detail on the reasons for the grounding.

Truck Passenger Killed In R44 Emergency Landing
Kate O'Connor

The passenger of a passing truck was killed when a Robinson R44 attempted to make an emergency landing on a road in Palm River, Florida, on Thursday afternoon. According to the Hillsborough County Sheriff's Office, one of the helicopter’s rotor blades broke off after hitting a telephone pole and struck the truck, killing the passenger. The driver of the truck was taken to a local hospital in unknown condition and one of the two pilots onboard the helicopter was hospitalized for “some heat exhaustion and some dehydration issues.” The identities of those involved have not yet been released.

The Sherriff’s Office reported that the helicopter suffered catastrophic engine failure while it was being transported to Sarasota after having been in for service. No further details have been given on what kind of maintenance was performed. As shown in the video below, the pilot was able to autorotate the helicopter enough to make a hard landing. The accident occurred at 2:21 p.m. local time on 50th Street at Palm River Road. The NTSB is investigating.

Levil Introduces Astro Link ADS-B In Module
Marc Cook

At Sun 'n Fun this week, Levil Avionics debuted a new ADS-B In receiver to drive various tablet-based systems with no-cost weather and traffic. In addition to the dual-band receiver, the Astro Link has a built-in WAAS GPS receiver and full AHRS module for attitude information. This allows the Astro Link to provide valuable backup attitude data to connected tablets.

The Astro Link leverages AHRS technology the company has developed for its certified offerings and adds the ADS-B receiver as justification for the $599 price tag. The box is a bit bigger than a deck of playing cards (4.3 by 3.2 by 1 inches) and contains all necessary antennas inside the case. It weighs less than a pound and comes with silicone bumpers to keep it from sliding off the glareshield. Connection to outboard apps is via Wi-Fi, not Bluetooth. It can support as many as six devices simultaneously.

CFIs Urged To Get Uncomfortable
Russ Niles

The Society of Aviation and Flight Educators (SAFE) is challenging CFIs young and old to sharpen their own hand flying skills to pass that knowledge along to students. In an announcement at Sun ’n Fun 2019 the national association of instructors said it’s launching the SAFE CFI-PRO workshop to reduce the number of inflight loss of control (LOC-I) accidents, the major cause of GA accidents and fatalities. “Every CFI really needs to be on top of his or her game,” said SAFE board member David St. George.

He said in a podcast interview It’s time the full spectrum of instructors, from newly certificated to veterans, took their stick and rudder skills for a spin to aid the national effort to reduce the number of loss-of-control accidents. The organization has designed a curriculum and a set of flight maneuvers for CFIs to practice and then use with students that will ultimately get them and their students out of their comfort zones. The first workshop will be held at AOPA headquarters in Frederick, Maryland, and all CFIs are welcome to sign up. A new website,, explains the program and will feature a registration function in coming weeks.

Podcast: GAMI's Tim Roehl Explains The New GAMISPEC 550 Engine Program
Marc Cook

In this podcast from Sun 'n Fun 2019, GAMI's Tim Roehl offers the details behind the new GAMISPEC 550 engines, gross-weight increases for various Bonanza models, and then offers an update on GAMI's unleaded avgas replacement.

Lycoming 'When can an engine give you 200 extra flying hours?'
Aircraft Makers Look To Carmakers For Inspiration
AVweb Staff

A persistent dream of aviation buyers is for airplanes to be as innovative as modern cars, with quality to match. With electric airplanes on the horizon and eVTOL aircraft a thing, that’s exactly what’s happening, according to Aviation Week’s MRO network.

Increasingly, aircraft companies are finding inspiration and product ideas in cutting-edge automotive technologies. Both Boeing and Airbus have paired with automotive vendors to help design components and systems. Boeing is getting help from seating specialist Adient, Mercedes-Benz and General Motors, while Airbus has paired with German automaker Audi.

The emerging urban mobility market is seen as having automotive-type volume, even though no such aircraft are nearing certification or market entry yet. “Independent studies of the UAM market suggest there will be the need for a significant number of these aircraft, meaning they will need to be produced at volumes more akin to those in the automotive sector,” a spokesman for Lilium told the publication. Lilium is one of many startup companies designing aircraft for the urban mobility market. Although these aircraft are expected to be electric, there’s been a notable shift toward hybrid designs because battery energy density is still too limited for practical range and endurance.

Airbus worked with Audi last summer to develop ground transportation for its on-demand helicopter booking platform called Voom. That service may be a precursor to a wider system of on-demand eVTOL aircraft that are expected to eventually be autonomous air taxis. Airbus introduced its CityAirbus eVTOL in March in Ingolstadt, Germany, Audi’s home base.

Podcast: Lightspeed Aviation Foundation
Kate O'Connor

The Lightspeed Aviation Foundation was founded in 2010 with the idea of finding ways to promote a vibrant general aviation community. Lightspeed Aviation founder and president Allan Schrader discussed the foundation and its recent initiative to support new pilots with AVweb at Sun 'n Fun 2019.

Most Memorable Av Records Of 2018
Tim Cole

Ever since Orville bet Wilbur he could squeeze out ten more feet on those first precarious runs at Kitty Hawk, aviators have been setting—and beating—records in the air. Not content with highest, fastest, longest, today’s aviation records include such obscurities as distance goals for RC aircraft and numbers of skydivers attempting a vertical formation.

The organization that compiles this information is the National Aeronautic Association, the official record keeper for aviation in the United States. NAA certified 99 national records last year. Those NAA milestones qualifying as world records were then ratified by the Federation Aeronautique Internationale (FAI). Of these, the “most memorable” were released during Sun 'n Fun.

They include:

Fastest glider over a 500-kilometer (310.7 statute mile) out-and-back course: 158.53 MPH, set by New Zealand’s Keith Essex, landing and departing from the Omarama airport on the South Island. The previous record was 139 MPH.

Fastest speed over a recognized course: 631.8 MPH, set by pilots Ross Oetjen, Tony Briotta and Todd Hicks in a Gulfstream G-500 from Seville, Spain, to Al Bateen Executive in Abu Dhabi, a distance of 3,632 miles. The flight took five hours and 45 minutes. There was no previous record along that route.

Fastest time to climb to 3,000 meters (9,842,52 feet): Less than 100 seconds, set by Daniel Gray over Oxnard, California, airport in a Harmon Rocket IIA. The Harmon Rocket is a clipped-wing RV-4 with a 650-HP rotary engine. The previous record was one minute, 59.5 seconds.

Largest formation sequence, head-down orientation, four formations: 42 skydivers over Ottowa, Illinois. Previous record, set in 2014, was 33 skydivers.

RC model aircraft distance goal and return: 33.9 miles, set by John McNeil along U.S. Route 93 near Majors Place, Nevada. McNeil piloted his RC helicopter from the back of moving pickup truck to a designated turning point 17 miles to the north, and returned. Previous record was set by McNeil in 2016 at 31 miles.

Highest absolute altitude for a glider: 74,334 feet, set by pilots Jim Payne and Tim Gardner over El Calafate, Argentina, aboard Perlan 2. The previous record was set in the same aircraft by the same pilots one month earlier with an ascent to 63,808 feet.

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Aviators Market Launches New Site
Kate O'Connor

Aviators Market Publishing announced the launch of at Sun ‘n Fun 2019. The new website, which has been under development for the last three years, will facilitate the buying and selling of all things aviation including aircraft, engines, avionics, aviation-related services and real estate. In addition to a variety of sorting and filtering features, the site allows shoppers to compare multiple listings, save selections to a “Dream List” and receive notifications for particular listings or sellers.

“While you can find anything related to aviation on the internet, that search is often a long and frustrating experience,” said Aviators Market Publishing CEO Ana Cunha-Fontes. “We did a lot of research and learned that what people want today is an easier, more personalized experience whenever they shop for anything online. That’s what lead to the creation of”

The site is split into separate sections for corporate and general aviation markets. The company says it intends to provide sellers and service providers on the site with “an array of new-generation tools to make their advertising more effective.” is also offering 24/7 live support by phone, online chat and email.

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