Tuesday, March 19, 2019

Ethiopian ET302 similarities to Lion Air JT610

Reports from Ethiopian investigators have implicated the same Angle of Attack (AoA) sensor malfunction that was observed on Lion Air. Lion Air captain AoA sensor read about 22 degrees higher than the First Officer AoA sensor (a large bias error). Initial assessment of Lion Air AoA failure modes did not reveal any obvious electrical malfunction that could create the bias. The simplest explanation was that the AoA vane had been bent, causing a gross aerodynamic offset in the readings. If ET302 encountered the exact same offset, with the likelihood of it being bent exactly the same way not being conceivable, some other factor must be in play. For example, the ARINC 429 representation of AoA uses two's complement fraction binary notation (BNR). It is interesting to note that bit 26 represents 22.5 degrees which would be the bit "flipping" between the Captain and F/O AoA values (all other bits would match).  Is it possible that the ARINC 429 word is getting corrupted (software defect)?  If the ET302 offset was something like 20 or 24, this theory falls apart.

With this in mind, what are the issues left to restore 737 MAX airworthiness?

Friday, March 15, 2019

What have we learned this week?

The crash of Ethiopian ET302 brought a tragic beginning to what must be one of the worst weeks in aviation, ending with the grounding of the Boeing 737 MAX. What does Lion Air JT043 and JT610 teach us? Did we, as an industry do everything we should after JT610? Accusations of impropriety levied at Boeing and the FAA seemingly are always on the ready. Adding to the week was an update on Atlas 5Y3591 which at first seemed to be one thing, but with a slight wording change thankfully seems to be another altogether.

Thursday, March 14, 2019

Comparing Ethiopian ET302 to Lion Air JT043, JT610

Did Ethiopian ET302 succumb to the same situation as Lion Air JT610? The FDR and CVR data is being processed as I write this, with a public release in some form expected by Monday March 18. Aviation authorities have grounded the Boeing 737 Max before receiving a report from this recorder data. The only information to the public is from commercial ADS-B data brokers, notably Flightradar24.com, whose recording is incomplete. Aireon has shared space-based ADS-B data with several parties, but not to the public. Canada and the US make reference to the Aireon data as a factor in their assessment, with the claim that there were sufficient similarities to be concerned.

Tuesday, March 12, 2019

Atlas Air 5Y3591 Dove because of Nose-Down Elevator Command

The NTSB has revealed that Atlas Air 767 Freighter flight 5Y3591 dove based on nose-down elevator command. The nose was pushed over 49 degrees nose down. The engines were brought up to full thrust. There was no stall warning that preceding these actions. The dive reached 430 knots before impacting. Pitch attitude rose from -49 deg. to -20 deg. in the dive.

Saturday, March 9, 2019

Exploring Rain Fade in an Extreme Rain Fall Zone

Rain Fade is a factor with Ku-band and Ka-band satellite communications.  Rainfall rate is measured in mm/hour. The occurrence of significant Rain Fade events is scaled by the rainfall rate and its duration. Generally these events are transient as the rain cloud moves through. The path of interest is only the line from the satcom terminal to the servicing satellite. Only while the rain cloud is in the way do problems occur.

Panama is in a very severe rainfall rate region and will create frequent issues with Ka band service operating below about 15,000 feet. Ku should operate through these scenarios with less disruption. It is prominent in the region along with the Brazilian rain forests and significant as a hub airport. 

Friday, March 8, 2019

5Y3591 Stabilizer Trim Actuator appears to be Nose Down

When KHOU took a video tour of the collected wreckage, they included a frame of the stabilizer trim actuator (the jackscrew).

Thursday, March 7, 2019

Limiting RF exposure to Humans in Close Proximity to Satellite Transmitters

Satellite radios produce powerful Radio Frequency (RF) emissions. A method is provided for limiting the RF exposure to humans that are in close proximity to satellite transmitter antennas by establishing radial keep-out zones.