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In the Boeing 737 MAX crisis we have extensive coverage from many affected stakeholders except the aeronautical engineers, who actually hold responsibility of every factor significant in the loss of 346 lives in the Lion Air 610 and Ethiopian 302 accidents:<\/p>\n
Added to those, FAA announced they recently discovered another weakness in the AFCS software, unrelated to the MCAS. This too may cause excessive pitch down under some exceptional circumstances and needs to be corrected.<\/p>\n
As an aeronautical engineer specialized in avionics, I am very worried and would like to make some points from this side.<\/p>\n
After FAA grounded the 737 MAX, Boeing came with a plan to fix the software, which made sense:<\/p>\n
The first two points imply software updates only and they seem straightforward to implement in a commensurate amount of time. They should have been ready many months ago.<\/p>\n
The third one also seems a simple software update issue. The data packs from both A-o-A sensors flow through the data buses of the aircraft, and can be routed in such a way that the MCAS uses both A-o-A indications to decide. For some surprising and unobvious reason, this is not so. The Boeing insiders claim the 737 MAX architecture does not allow both sensors to be used in the control loop, so the architecture itself needs an overhaul. I cannot imagine an architecture preventing a piece of software to fetch significant data packs from a data bus, since there is one data bus common to both aircraft port and starboard (in fact they are two buses for redundancy, but they are both common). This technical issue is beyond the extent of my imagination, and I hope someone from inside (Boeing or Collins) would explain it more clearly. Moreover, if this is architecture schizophrenia is true, how comes the A-o-A disagree function operates at all?<\/p>\n
This third issue alone is the probable cause for such a long delay of 737 MAX grounding. If the architecture needs to be rethought, this is a time bomb, could take time to design, implement, test, and certify.<\/p>\n
Besides these MCAS related problems, it seems that other two issues came up to add uncertainty:<\/p>\n
This latter objection of FAA back in 2017 was ignored by Boeing at the time, 6 months late in the Airbus A320Neo catch up game. Now, the objection resurfaced, and according to the new FAA Administrator, there is plenty of time to fix everything, since there is no time limit to the 737 MAX grounding. Technically, the rudder cables problem is way much harder to fix than the other software or even hardware issues. Is there a real risk with the 737 MAX rudder cables? Or was it just excessive prudence from the regulators back in 2017, now just pouring gas on the fire? If someone asked this question before Southwest 3472 uncontained engine failure in 2016, maybe my answer would have been different. In the meantime we also had Southwest 1380 in 2018, a strikingly similar uncontained engine failure affecting another 737 NG. We also have to bear in mind that 14% cut in fuel consumption in the new LEAP-1 737 MAX engine is pushing the envelope even further. As low as it is, the risk of an uncontained engine failure was not reduced in LEAP-1 as compared to CFM-56. If this low risk could compromise the lateral controllability of the airplane, it needs to be mitigated.<\/p>\n
Returning to MCAS, I will try to solve a mystery. Since Boeing announced that they will limit the authority of MCAS, how is it going to cope with real high Angle-of-Attack situations? What justified such a forceful reaction of MCAS initially? Another mystery of the MCAS design is the 10 seconds on – 5 seconds off logic, using aerodynamic feedback only, based on a single A-o-A sensor only. If one moves the horizontal stabilizer of a 737 fully downwards (and this is acknowledged by the stabilizer pitch angle sensor feedback) and if the aerodynamic feedback (A-o-A sensor) gives nothing, not the slightest nose down, what scenario could justify the 10-5 algorithm? Why repeat this action in a loop, since the unique explanation of such a behaviour is a faulty A-o-A sensor? Why disregard completely the pitch angle of the aircraft at \u221240\u00b0 while you try to avoid an extreme high angle of attack? Why is the pitch angle not part of the aerodynamic feedback, such as in the autopilot design? Too many questions here, I wish I could answer to for my students.<\/p>\n
Regarding the abusive authority of the initial MCAS design, our picture shows what happened when the larger diameter engines were fitted under the wings of 737 MAX. The engines were moved a bit forward with respect to the wing, and their geometric centre was placed slightly lower. Some sources even say it was placed slightly higher! This contradiction can be explained: the larger diameter engine appears to be higher at the intake and on the ground (due to the extension of the landing gear by 0.4 m), but the geometric centre of the engine is approximately 4% lower than the aircraft centre of gravity. We are comparing the 737 MAX family aircraft with the previous 737 NG family, which did not require MCAS or an equivalent of MCAS. MCAS was supposed to compensate for the pitch up effect of the 737 MAX at high angle of attack attitudes. Why does this pitch up effect appear in case of 737 MAX?<\/p>\n
In the first place, if the engines were higher, the upward momentum of the thrust force would have been lower than at the 737 NG. So forget it, it is lower 4%, but 4% is not such a scary change. What about mounting the engines further to the front? What does it do to the thrust force upward momentum? Well, nothing. The momentum of a force is the force multiplied by the distance of the centre to the direction of the force. Moving the engines front or aft does not change the momentum. So geometry does not really explain the necessity of MCAS. What then?<\/p>\n
Contrary to most sources (including my own article Legendary Safety of Boeing 737 Family<\/a>, where I was superficially adopting the general current of opinion), it is not the engine geometry that justified the MCAS solution. There are two other factors which push the nose up when throttling up from a high angle of attack situation:<\/p>\n The pitch up rotation momentum M<\/em><\/strong>theta<\/sub><\/strong> is strictly T<\/strong>\u00d7<\/strong>d<\/em><\/strong> and thus is not directly influenced by front-aft movements of the engines. Also, I have to disappoint the Internet experts who claim that in high Angle-of-Attack situations, the engines push a lot of air and exhaust gas down and that is why the aircraft pitches up more. T<\/strong>\u00d7<\/strong>d<\/em><\/strong> for the 737 MAX is not greater than 1.1\u00d71.04 = 1.14 times the momentum for 737 NG. Adding the extra lift of the larger engines nacelles, the pitch up momentum does not look like more than 17% as compared to the unprotected B737 NG. Thus, I can hardly find any justification for the disproportionate authority that the initial MCAS was designed with. A large margin design is not a good design practice in aerospace engineering. Excessive structural resilience or excessive actuating forces do not indicate good engineering practice in aerospace, in contrast to other fields of engineering. Aerospace is on the edge, so doing too much good is hurting someone.<\/p>\n Regarding the blame attributed to the pilots in both accidents, we should make it very clear once and for all that in both accidents, pilots were not to blame. Blaming the pilots was a mistake. It is very easy to understand by following YouTube demos in flight simulators what the pilots went through in both accidents[2]<\/a>.<\/p>\n Another issue is that the MCAS represents the ending of the era of Boeing airplanes as pilot\u2019s airplanes. Airbus has the Fly-By-Wire philosophy since the 1980s, so basically flying the aircraft is the job of robots who decide what to do. Human pilots just tell the robots what they want, but they have no veto on the robots. Perpignan A320 accident is the story of a bad decision by the robots, while excellent human pilots on board of that aircraft contemplated the disaster, since they could not take over from the suicidal robots. To do them justice, the robots were misled by two simultaneously faulty A-o-A sensors (in agreement), which were blocked due to incorrect washing of the airplane prior to the flight with water under pressure. The cause of the Perpignan accident was a fatal mistake made by the personnel on the ground, prior to the flight.<\/p>\n By nature, Boeing 737 is different. Pilots can veto any automated system in all 737 families, except for 737 MAX and except for the robot called MCAS. When this robot takes over, it could kill everyone without any way for the human pilots to intervene. This is yet another unexpected feature for experienced Boeing pilots. A Boeing 737 pilot is in control of the airplane, and if a function is delegated to an automated system, this can be cut off in case anything wrong happens, unlike the Airbus pilot. MCAS philosophy violates this principle. Of course, if Airbus is violating this principle and keeps flying successfully for the past 30 years, why Boeing would not be allowed to, just a bit?<\/p>\n The MCAS design now openly explained, Boeing pilots understand that they have a fellow robot in the cockpit who can take control. Sadly, this robot cannot be stopped if it goes out of its mind. The robot points to the ground for 10 seconds, releases pressure for 5 seconds and repeats. Airbus pilots know they have these beasts on board, got used to them, and 30 years of safe operation raised the confidence in the reliability of their robots. Even too much so, because when Airbus pilots are deprived of the functions of the robots, sometimes they unexpectedly fail on the manual control (AFR 447, AirAsia 8501). This phenomenon is called overreliance on automation<\/em>. However, Boeing pilots are entitled to their sovereignty in the cockpit, this is fundamental of their flying culture.<\/p>\n MCAS is not only a robot who failed twice due to a faulty sensor. MCAS is an overturn of an aircraft control philosophy. This raises a worrying question: how could FAA agree to extend an airworthiness type certificate issued in 1967 for Boeing 737-100 and 737-200 down to 737 MAX, since 737 MAX includes a revolutionary flight control philosophy? This was not explained to the pilots (in fact not even to FAA as it turns out), making the issue of fixing the MCAS even more problematic.<\/p>\n In our opinion, a FBW aircraft requires a separate certification process, even though it is aerodynamically identical to a classic aircraft.\u00a0 Also, a non FBW aircraft which includes at least one augmentation system which takes over and cannot be switched off, such as the MCAS, becomes a de facto FBW aircraft. This species could be called Sometimes-Fly-By-Wire (SFBW). However, the presence on board of an automated decision maker, totally changes the processes and the culture in the cockpit. Boeing 737 pilots were not prepared for that change.<\/p>\n In conclusion, the situation of Boeing 737 MAX is less bright than expected. My previous piece on the subject demonstrates excessive optimism in hindsight. As always, things are more complex than they appear.<\/p>\n One lesson that I get from here is that avionics engineers should be aerospace engineers and not electronics \/ computer engineers or even worse, software programmers. These people need to understand fully how and why does an aircraft fly and what are all possible consequences of their software and hardware design and malfunctions. They should be educated in the cult of absolute responsibility and in the spirit of low margin aerospace engineering. They should understand human pilots, and even more than that, they should fly airplanes themselves. Without being a pilot, at least occasionally, one will never make a good avionics engineer or aeronautical engineer. (Due to objective reasons, astronautics engineering is exempt).<\/p>\n Aerospace engineering has shifted its centre of gravity over the years from mechanical engineering into electrical engineering (while spreading over both though). Aerospace engineering schools have to adapt to this reality, instead of leaving computer engineering schools to fill the gap. The reason for that is explained in another piece of mine (3DEXPERIENCE: The New French Revolution<\/a>).<\/p>\n Certification process of a new type of aircraft should be taken very seriously. FAA, EASA and other national authorities have a major responsibility to the flying public, otherwise the confidence in air travel gets thin, in spite of the asymmetrical efforts for superb safety performance that this industry is capable of. My opinion is that EASA should have been particularly pro-active with 737 MAX cutting corners of certification. EASA should watch FAA and vice versa, they should back each other up. Apart from grounding the plane two days earlier, EASA did not do much on the 737 MAX. If I can understand the delegation principle and the motivation of the FAA to promote US aircraft types, EASA should be motivated differently, and thus provide some balance. EASA issued their certificate for 737 MAX types on 27 March 2017, only 19 days after FAA. Was this rush really necessary?<\/p>\n [1]<\/a> „MCAS can never command more stabilizer input than can be counteracted by the flight crew pulling back on the column. The pilots will continue to always have the ability to override MCAS and manually control the airplane.” from Boeing 737 MAX Updates published by Boeing<\/p>\n [2]<\/a> https:\/\/www.youtube.com\/watch?v=OxPsxmU_ocI<\/a><\/p>\n [\/et_pb_text][et_pb_divider color=”rgba(147,175,193,0.39)” show_divider=”on” divider_style=”solid” divider_position=”top” hide_on_mobile=”on” \/][et_pb_comments show_avatar=”on” show_reply=”on” show_count=”off” background_layout=”light” use_border_color=”off” border_color=”#ffffff” border_style=”solid” custom_button=”off” button_letter_spacing=”0″ button_use_icon=”default” button_icon_placement=”right” button_on_hover=”on” button_letter_spacing_hover=”0″ \/][\/et_pb_column_inner][\/et_pb_row_inner][\/et_pb_column][et_pb_column type=”1_4″][et_pb_blog fullwidth=”off” include_categories=”11″ show_thumbnail=”off” show_content=”off” show_more=”off” show_author=”on” show_date=”on” show_categories=”off” show_comments=”off” show_pagination=”on” offset_number=”0″ use_overlay=”off” background_layout=”light” use_dropshadow=”on” use_border_color=”on” border_color=”#e5e5e5″ border_style=”solid” \/][\/et_pb_column][\/et_pb_section]<\/p>\n","protected":false},"excerpt":{"rendered":" In the Boeing 737 MAX crisis we have extensive coverage from many affected stakeholders except the aeronautical engineers, who actually hold responsibility of every factor significant in the loss of 346 lives in the Lion Air 610 and Ethiopian 302 accidents: Design of an unsafe (single-point-of failure) augmentation system: the MCAS Self-certification of the aircraft […]<\/p>\n","protected":false},"author":5,"featured_media":21681,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"on","_et_pb_old_content":" [et_pb_section bb_built=\"1\" fullwidth=\"off\" specialty=\"on\"][et_pb_column type=\"3_4\" specialty_columns=\"3\"][et_pb_row_inner admin_label=\"Row\"][et_pb_column_inner type=\"4_4\" saved_specialty_column_type=\"3_4\"][et_pb_text background_layout=\"light\" text_orientation=\"justified\" use_border_color=\"off\" border_color=\"#ffffff\" border_style=\"solid\" _builder_version=\"3.0.92\"]<\/p> \u00cen desf\u0103\u0219urarea crizei Boeing 737 MAX avem \u00een media o foarte bun\u0103 acoperire a opiniilor tuturor celor interesa\u021bi de acest caz, cu excep\u021bia inginerilor de avia\u021bie, care de fapt poart\u0103 responsabilitatea pentru fiecare din factorii cauzali semnificativi pentru pierderea celor 346 de vie\u021bi \u00een accidentele Lion Air 610 \u0219i Ethiopian 302:<\/p> Peste toate acestea, FAA a anun\u021bat recent descoperirea unei alte sl\u0103biciuni \u00een software-ul AFCS, f\u0103r\u0103 leg\u0103tur\u0103 cu MCAS. Aceasta de asemenea poate cauza un tangaj negativ excesiv \u00een anumite circumstan\u021be excep\u021bionale, necesit\u00e2nd s\u0103 fie corectat\u0103.<\/p> Ca inginer de avia\u021bie specializat \u00een avionic\u0103, sunt foarte \u00eengrijorat \u0219i a\u0219 dori s\u0103 punctez c\u00e2teva lucruri din punctul meu de vedere.<\/p> Dup\u0103 oprirea la sol a avioanelor 737 MAX, Boeing a venit cu un plan plauzibil de a modifica software-ul:<\/p> Primele dou\u0103 puncte implic\u0103 doar actualiz\u0103ri de software \u0219i par simplu de implementat \u00eentr-o perioad\u0103 comensurabil\u0103 de timp. Ar fi trebuit s\u0103 fie gata acum mai multe luni de zile. A treia pare de asemenea s\u0103 fie o banal\u0103 actualizare de software. Pachetele de date de la ambii senzori A-o-A circul\u0103 prin magistralele de date ale aeronavei \u0219i pot fi rutate \u00een a\u0219a fel \u00eenc\u00e2t MCAS s\u0103 foloseasc\u0103 indica\u021biile ambilor senzori A-o-A. Din motive surprinz\u0103toare \u0219i neevidente, lucrurile nu stau a\u0219a. Surse din interior pretind c\u0103 arhitectura 737 MAX nu permite utilizarea ambilor senzori \u00eentr-o bucl\u0103 de control, deci arhitectura \u00eens\u0103\u0219i ar trebui ref\u0103cut\u0103. Nu-mi pot imagina o arhitectur\u0103 care s\u0103 \u00eempiedice un software s\u0103-\u0219i extrag\u0103 pachetele de date necesare dintr-o magistral\u0103 de date, din moment ce exist\u0103 o magistral\u0103 de date comun\u0103 at\u00e2t pentru tribordul c\u00e2t \u0219i pentru babordul aeronavei (de fapt sunt dou\u0103 magistrale pentru redundan\u021b\u0103, dar ambele au acoperire general\u0103). Aceast\u0103 problem\u0103 tehnic\u0103 dep\u0103\u0219e\u0219te limitele imagina\u021biei mele \u0219i sper ca oameni din interior (Boeing sau Collins) s\u0103 explice mai clar despre ce este vorba. Mai mult dec\u00e2t at\u00e2t, dac\u0103 aceast\u0103 schizofrenie arhitectural\u0103 este adev\u0103rat\u0103, cum poate func\u021biona modulul de Dezacord A-o-A?<\/p> Aceast\u0103 a treia problem\u0103 singur\u0103 este probabil cauza unei prelungiri at\u00e2t de mari a opririi la sol a tipurilor 737 MAX. Dac\u0103 arhitectura trebuie reg\u00e2ndit\u0103, aceasta este o bomb\u0103 de timp, ar putea dura mult proiectarea, implementarea, testarea \u0219i certificarea.<\/p> \u00cen afar\u0103 de aceste probleme legate de MCAS, se pare c\u0103 mai exist\u0103 dou\u0103 chestiuni care adaug\u0103 incertitudine:<\/p> Aceast\u0103 obiec\u021bie din urm\u0103 a FAA din 2017 a fost ignorat\u0103 de Boeing la timpul respectiv, fiind cu 6 luni \u00een \u00eent\u00e2rziere fa\u021b\u0103 de rivalul Airbus A320Neo. Acum, obiec\u021bia a ie\u0219it la suprafa\u021b\u0103 \u0219i, conform noului Administrator al FAA, avem timp s\u0103 punem totul la punct, deoarece nu exist\u0103 o limit\u0103 impus\u0103 pentru oprirea la sol a tipurilor 737 MAX. Tehnic, problema cablurilor de palonier este mult mai greu de rezolvat dec\u00e2t celelalte probleme de software, chiar \u0219i de hardware. Este un risc real la 737 MAX cu cablurile de palonier? Sau este doar pruden\u021b\u0103 excesiv\u0103 din partea regulatorilor atunci \u00een 2017, pun\u00e2ndu-se acum gaz peste foc? Dac\u0103 cineva m-ar fi \u00eentrebat acest lucru \u00eenainte de accidentul Southwest 3472 cu defec\u021biune exploziv\u0103 de motor \u00een 2016, probabil c\u0103 a\u0219 fi r\u0103spuns altfel. \u00centre timp \u00eens\u0103 s-a ad\u0103ugat \u0219i Southwest 1380 \u00een 2018, o defec\u021biune exploziv\u0103 \u0219ocant de similar\u0103, afect\u00e2nd tot un 737 NG. De asemenea, s\u0103 \u021binem cont c\u0103 reducerea de consum de combustibil cu 14% la noul motor LEAP-1 737 MAX \u00eempinge anvelopa \u0219i mai tare. Chiar dac\u0103 este infim, riscul unei defec\u021biuni explozive de motor nu a fost redus la LEAP-1 \u00een compara\u021bie cu CFM-56. Dac\u0103 acest risc infim ar putea afecta controlabilitatea lateral\u0103 a avionului, m\u0103surile de atenuare a riscurilor se impun.<\/p> \u00centorc\u00e2ndu-ne la MCAS, s\u0103 \u00eencerc\u0103m s\u0103 solu\u021bion\u0103m un mister. Din moment ce Boeing au anun\u021bat c\u0103 vor limita autoritatea MCAS-ului, cum se va mai descurca acesta \u00eentr-o situa\u021bie de veritabil unghi de atac mare? Ce a justificat o asemenea for\u021b\u0103 de reac\u021bie a MCAS-ului ini\u021bial? Un alt mister al proiect\u0103rii MCAS-ului const\u0103 \u00een logica de cuplare timp de 10 secunde \u2013 decuplare 5 secunde, folosind doar feedback aerodinamic, pe baza doar a senzorului A-o-A st\u00e2ng. Dac\u0103 stabilizatorul orizontal al unui 737 este bracat complet \u00een jos (\u0219i acest lucru este verificat prin bucla de reac\u021bie pe senzorul de pozi\u021bie unghiular\u0103 de bracaj) \u0219i dac\u0103 \u00een bucla de reac\u021bie aerodinamic\u0103 (senzorul A-o-A) nu se \u00eenregistreaz\u0103 nicio schimbare, nici cea mai mic\u0103 reducere de unghi, ce scenariu ar putea justifica algoritmul 10-5? De ce s\u0103 repe\u021bi \u00een bucl\u0103 aceast\u0103 opera\u021biune, din moment ce unica explica\u021bie a unui astfel de comportament este un senzor A-o-A defect? De ce s\u0103 treci cu vederea aducerea aeronavei la un unghi de tangaj de \u221240\u00b0 \u00een condi\u021biile \u00een care totul este despre evitarea unor situa\u021bii cu unghi de atac neobi\u0219nuit de mare? De ce din feedback-ul aerodinamic nu face parte \u0219i unghiul de tangaj, a\u0219a cum se \u00eent\u00e2mpl\u0103 la pilotul automat? Prea multe \u00eentreb\u0103ri aici, ale c\u0103ror r\u0103spunsuri a\u0219 fi vrut s\u0103 le am, pentru studen\u021bii mei.<\/p> Referitor la autoritatea abuziv\u0103 a MCAS-ului \u00een versiunea ini\u021bial\u0103, diagrama noastr\u0103 ilustreaz\u0103 ce s-a \u00eent\u00e2mplat c\u00e2nd 737 MAX a trebuit echipat cu motoare cu diametru mai mare sub arip\u0103. Motoarele au fost mutate un pic \u00een fa\u021b\u0103 \u00een raport cu aripa \u0219i centrul lor geometric a fost cobor\u00e2t un pic. Unele surse pretind c\u0103 dimpotriv\u0103, au fost mutate mai sus. Aceast\u0103 contradic\u021bie poate fi explicat\u0103: diametrul mai mare al motorului \u00eel face s\u0103 par\u0103 mai sus la partea de sus a nacelei, c\u00e2nd aeronava este la sol (datorit\u0103 extensiei cu 0,4 m a trenului de aterizare), dar fa\u021b\u0103 de centrul de greutate al aeronavei, centrul geometric al motorului este cu aproximativ 4% mai jos. Compar\u0103m aici avioanele familiei 737 MAX cu familia precedent\u0103 737 NG, care nu a avut nevoie de MCAS sau de ceva echivalent. MCAS-ul ar fi trebuit s\u0103 compenseze efectul momentului de tangaj pozitiv al 737 MAX \u00een atitudini cu unghi de atac excesiv. De ce apare acest efect de moment de tangaj pozitiv la 737 MAX?<\/p> \u00cen primul r\u00e2nd, dac\u0103 motoarele ar fi fost amplasate mai sus, momentul pozitiv al for\u021bei de trac\u021biune ar fi fost mai mic dec\u00e2t la 737 NG. Deci s\u0103 uit\u0103m asta, amplasamentul este cu 4% mai jos, dar 4% nu este o schimbare chiar at\u00e2t de terifiant\u0103. Ce putem spune despre mutarea motoarelor mai \u00een fa\u021b\u0103? Ce efect are acest lucru asupra momentului de tangaj pozitiv? Ei bine, niciunul. Momentul unei for\u021be este for\u021ba \u00eenmul\u021bit\u0103 cu bra\u021bul, adic\u0103 distan\u021ba de la centrul de rota\u021bie la direc\u021bia for\u021bei. Mutarea motoarele \u00een fa\u021b\u0103 sau \u00een spate nu modific\u0103 momentul. Deci geomteria nu explic\u0103 \u00een realitate necesitatea MCAS-ului. Ce anume totu\u0219i?<\/p> Contrar mai multor surse (incluz\u00e2nd \u0219i propriul meu articol Siguran\u021ba legendar\u0103 a familiei Boeing 737<\/a>, unde am adoptat cu superficialitate curentul general de opinie), nu geometria motoarelor a justificat solu\u021bia MCAS. Mai exist\u0103 doi factori care \u00eemping botul \u00een sus c\u00e2nd sunt b\u0103gate motoarele \u00een plin \u00eentr-o situa\u021bie cu unghi de atac mare:<\/p> Momentul de rota\u021bie de tangaj pozitiv M<\/em><\/strong>theta<\/sub><\/strong> este strict T<\/strong>\u00d7<\/strong>d<\/em><\/strong> \u0219i astfel nu este direct influen\u021bat de amplasarea motoarelor fa\u021b\u0103-spate. De asemenea, trebuie s\u0103-i dezam\u0103gesc pe exper\u021bii din Internet care pretind c\u0103 \u00een situa\u021biile cu mare unghi de atac, deoarece motoarele \u00eemping mult aer \u0219i gaze de ardere \u00een jos, din aceas\u0103 cauz\u0103 cre\u0219te unghiul de tanga mai mult. T<\/strong>\u00d7<\/strong>d<\/em><\/strong> la 737 MAX nu este mai mare dec\u00e2t de 1.1\u00d71.04 = 1.14 ori momentul de la 737 NG. Chiar ad\u0103ug\u00e2nd portan\u021ba suplimentar\u0103 a motoarelor cu nacele mai mari, momentul de tangaj pozitiv nu pare s\u0103 dep\u0103\u0219easc\u0103 17% \u00een compara\u021bie cu neprotejatul B737NG. Astfel, nu prea g\u0103sesc justificare pentru autoritatea dispropor\u021bionat\u0103 a versiunii ini\u021biale de MCAS. Proiectarea cu toleran\u021be mari nu constituie o bun\u0103 practic\u0103 \u00een ingineria aerospa\u021bial\u0103. Rezisten\u021ba structural\u0103 excesiv\u0103 sau for\u021bele de ac\u021bionare excesive nu sunt un semn de bun\u0103 practic\u0103 \u00een ingineria aerospa\u021bial\u0103, \u00een contrast cu alte domenii ale ingineriei. Aeronautica \u0219i astronautica sunt la frontiera posibilului, deci facerea de bine excesiv \u00eenseamn\u0103 un r\u0103u \u00een alt\u0103 parte.<\/p> Referitor la culpa atribuit\u0103 pilo\u021bilor \u00een ambele accidente, ar trebui s\u0103 clarific\u0103m odat\u0103 pentru totdeauna c\u0103 \u00een niciunul din accidente pilo\u021bii nu au avut nicio vin\u0103. \u00cenvinov\u0103\u021birea pilo\u021bilor a fost o eroare. Putem \u00een\u021belege foarte simplu prin ce au trecut ace\u0219ti pilo\u021bi dac\u0103 urm\u0103rim pe YouTube reconstituirea \u00een simulator[2]<\/a>.<\/p> O alt\u0103 problem\u0103 este c\u0103 MCAS-ul semnific\u0103 sf\u00e2r\u0219itul erei \u00een care avioanele Boeing erau avioanele pilo\u021bilor. Airbus are filosofia Fly-By-Wire (FBW) din anii 1980, deci esen\u021bialmente pilotajul aeronavei este treaba unor robo\u021bi care decid ce trebuie s\u0103 fac\u0103. Pilo\u021bii umani doar comunic\u0103 robo\u021bilor ce anume ar dori, dar nu au veto asupra robo\u021bilor. Accidentul A320 de la Perpignan este povestea unei decizii nefericite a robo\u021bilor, cu excelen\u021bii pilo\u021bi umani r\u0103m\u00e2n\u00e2nd doar martori neputincio\u0219i la dezastru, f\u0103r\u0103 s\u0103 poat\u0103 prelua comanda de la robo\u021bii sinuciga\u0219i. Ca s\u0103 le facem dreptate \u0219i acestor robo\u021bi, ei au fost indu\u0219i \u00een eroare de doi senzori A-o-A simultan bloca\u021bi (care nu erau \u00een dezacord), din cauza sp\u0103l\u0103rii incorecte a avionului \u00eenainte de zbor cu ap\u0103 sub presiune. Cauza accidentului de la Perpignan a fost o gre\u0219eal\u0103 fatal\u0103 comis\u0103 de personalul de sol, \u00eenainte de zbor.<\/p> Prin natura sa, Boeing 737 este diferit. Pilo\u021bii au veto asupra oric\u0103rui sistem automat la toate familiile 737, cu excep\u021bia 737 MAX \u0219i cu excep\u021bia robotului denumit MCAS. C\u00e2nd acest robot preia conducerea, poate ucide pe toat\u0103 lumea f\u0103r\u0103 s\u0103 mai poat\u0103 interveni cineva. Aceasta este o alt\u0103 supriz\u0103 nepl\u0103cut\u0103 pentru pilo\u021bii Boeing 737 cu experien\u021b\u0103. Un pilot Boeing 737 are controlul asupra aeronavei \u0219i dac\u0103 deleag\u0103 o func\u021bie unui sistem automat, acesta poate fi dezactivat oric\u00e2nd dac\u0103 apare un pericol, spre deosebire de un pilot Airbus. Filosofia MCAS \u00eencalc\u0103 acest principiu. Desigur, dac\u0103 Airbus \u00eencalc\u0103 aceste principiu de 30 de ani \u0219i continu\u0103 s\u0103 zboare \u00een siguran\u021b\u0103, de ce nu ar putea \u0219i Boeing, m\u0103car un pic?<\/p> Acum c\u00e2nd proiectarea MCAS este explicat\u0103 public, pilo\u021bii Boeing \u00een\u021beleg c\u0103 au \u00een cockpit un coleg robot, care poate prelua controlul. Din p\u0103cate, acest robot nu poate fi oprit dac\u0103 \u00ee\u0219i iese din min\u021bi. Robotul bag\u0103 avionul \u00een picaj pentru 10 secunde, se calmeaz\u0103 5 secunde apoi repet\u0103. Pilo\u021bii Airbus \u0219tiu c\u0103 au aceste creaturi la bord, s-au obi\u0219nuit cu ele \u0219i 30 de ani de opera\u021biuni \u00een siguran\u021b\u0103 au elevat \u00eencrederea \u00een fiabilitatea robo\u021bilor respectivi. Chiar prea mult, pentru c\u0103 atunci c\u00e2nd pilo\u021bii Airbus sunt priva\u021bi de func\u021biuni ale robo\u021bilor lor, uneori total surprinz\u0103tor e\u0219ueaz\u0103 \u00een controlul manual (AFR 447, AirAsia 8501). Acest fenomen se nume\u0219te overreliance on automation<\/em>. Totu\u0219i, pilo\u021bii Boeing sunt \u00eendrept\u0103\u021bi\u021bi la suveranitatea lor \u00een cockpit, acest lucru este fundamental pentru cultura lor de zbor.<\/p> MCAS nu este doar un robot care a gre\u0219it de dou\u0103 ori din cauza unui senzor defect. MCAS este o r\u0103sturnare a unei filosofii de control al aeronavei. Apare o \u00eentrebare \u00eengrijor\u0103toare: cum a fost de acord FAA s\u0103 extind\u0103 un certificat de navigabilitate de tip emis \u00een 1967 pentru Boeing 737-100 \u0219i 737-200 p\u00e2n\u0103 la 737 MAX, din moment ce 737 MAX include o filosofie de control al zborului revolu\u021bionar\u0103. Aceasta nu a fost explicat\u0103 pilo\u021bilor (de fapt a\u0219a cum se pare, nici m\u0103car FAA-ului), f\u0103c\u00e2nd din aceast\u0103 chestiune a repar\u0103rii MCAS-ului una \u0219i mai problematic\u0103.<\/p> \u00cen opinia noastr\u0103, un avion FWB necesit\u0103 un proces de certificare separat, chiar dac\u0103 este identic aerodinamic cu un avion clasic. De asemenea, dac\u0103 un avion non-FBW include m\u0103car un sistem de augmentare care preia controlul \u0219i nu poate fi decuplat, a\u0219a ca MCAS, devine de facto un avion FBW. \u00a0Aceast\u0103 specie s-ar putea denumi Sometimes-Fly-By-Wire (SFBW). Totu\u0219i, prezen\u021ba la bord a unui decident automat schimb\u0103 totalmente procesul \u0219i cultura \u00een cockpit. Pilo\u021bii Boeing 737 nu erau preg\u0103ti\u021bi pentru aceast\u0103 schimbare.<\/p> \u00cen concluzie, situa\u021bia Boeing-ului 737 MAX este mai pu\u021bin str\u0103lucit\u0103 dec\u00e2t p\u0103rea. Privit retrospectiv, articolul meu precedent pe subiect demonstreaz\u0103 optimism excesiv. Ca \u00eentotdeauna, lucrurile sunt mai complicate dec\u00e2t aparen\u021bele.<\/p> O lec\u021bie pe care eu o extrag de aici este c\u0103 inginerii de avionic\u0103 ar trebui s\u0103 fie ingineri aerospa\u021biali \u0219i nu ingineri electroni\u0219ti sau de calculatoare, sau \u0219i mai r\u0103u, programatori. Ace\u0219ti oameni trebuie s\u0103 \u00een\u021beleag\u0103 pe deplin cum \u0219i de ce zboar\u0103 o aeronav\u0103 \u0219i care sunt toate consecin\u021bele posibile ale proiect\u0103rii software \u0219i hardware \u0219i ale func\u021bion\u0103rii incorecte a sistemelor. Ei trebuie educa\u021bi \u00een cultul responsabilit\u0103\u021bii absolute \u0219i \u00een spiritul ingineriei aerospa\u021biale cu coeficien\u021bi mici de siguran\u021b\u0103. Ei ar trebui s\u0103-i \u00een\u021beleag\u0103 pe pilo\u021bii umani, chiar mai mult dec\u00e2t at\u00e2t, ei ar trebui s\u0103 piloteze ei \u00een\u0219i\u0219i. F\u0103r\u0103 s\u0103 fii pilot, m\u0103car ocazional, nu po\u021bi deveni niciodat\u0103 un bun inginer de avionic\u0103 sau de aeronautic\u0103. (Din motive obiective, \u00een ingineria astronautic\u0103 nu putem cere acela\u0219i lucru).<\/p> De-a lungul anilor, ingineria aerospa\u021bial\u0103 \u0219i-a mutat centrul de gravita\u021bie de la ingineria mecanic\u0103 spre ingineria electric\u0103 (fiind \u00eempr\u0103\u0219tiat\u0103 totu\u0219i \u00een ambele). \u0218colile de inginerie aerospa\u021bial\u0103 trebuie s\u0103 se adapteze acestei realit\u0103\u021bi, \u00een loc s\u0103 lase \u0219colilor de ingineria computerelor s\u0103 umple golul. Ra\u021biunea pentru aceasta este explicat\u0103 \u00eentr-un alt articol al meu (3DEXPERIENCE: Noua Revolu\u021bie Francez\u0103<\/a>).<\/p> Procesul de certificare a unui nou tip de aeronav\u0103 trebuie luat foarte \u00een serios. FAA, EASA \u0219i alte autorit\u0103\u021bi na\u021bionale au o responsabilitate major\u0103 fa\u021b\u0103 de publicul care c\u0103l\u0103tore\u0219te cu avionul, altfel \u00eencrederea \u00een transportul aerian se sub\u021biaz\u0103, \u00een ciuda eforturilor asimetrice pentru superba performan\u021b\u0103 de siguran\u021b\u0103 de care industria este capabil\u0103. P\u0103rerea mea este c\u0103 EASA ar fi trebuit s\u0103 fie \u00een mod special pro-activ\u0103 cu cazul 737 MAX \u0219i scurt\u0103turile pe care a apucat certificarea acestuia. EASA trebuie s\u0103 supravegheze FAA \u0219i viceversa, ele trebuie s\u0103 se verifice una pe alta. \u00cen afar\u0103 de a opri la sol avioanele cu dou\u0103 zile mai devreme, EASA nu a muncit prea mult la 737 MAX. Dac\u0103 pot \u00een\u021belege principiul deleg\u0103rii \u0219i motiva\u021bia FAA de a promova tipurile de avion americane, EASA are o motiva\u021bie diferit\u0103 \u0219i astfel ar putea furniza un anumit echilibru. EASA au emis certificatul lor de navigabilitate pentru tipurile 737 MAX pe 27 martie 2017, la doar 19 zile dup\u0103 FAA. Era graba asta chiar necesar\u0103?<\/p> [1]<\/a> \"MCAS nu va mai putea comanda stabilizatorului mai mult bracaj dec\u00e2t cel care poate fi contracarat de pilo\u021bi prin tragerea de man\u0219\u0103. Pilo\u021bii vor continua \u00een orice situa\u021bie s\u0103 aib\u0103 posibilitatea s\u0103 dep\u0103\u0219easc\u0103 MCAS \u0219i s\u0103 controleze manual avionul.\" din Boeing 737 MAX Updates publicat de Boeing<\/p> [2]<\/a> https:\/\/www.youtube.com\/watch?v=OxPsxmU_ocI<\/a><\/p> [\/et_pb_text][et_pb_divider color=\"rgba(147,175,193,0.39)\" show_divider=\"on\" divider_style=\"solid\" divider_position=\"top\" hide_on_mobile=\"on\" \/][et_pb_comments show_avatar=\"on\" show_reply=\"on\" show_count=\"off\" background_layout=\"light\" use_border_color=\"off\" border_color=\"#ffffff\" border_style=\"solid\" custom_button=\"off\" button_letter_spacing=\"0\" button_use_icon=\"default\" button_icon_placement=\"right\" button_on_hover=\"on\" button_letter_spacing_hover=\"0\" \/][\/et_pb_column_inner][\/et_pb_row_inner][\/et_pb_column][et_pb_column type=\"1_4\"][et_pb_blog fullwidth=\"off\" include_categories=\"11\" show_thumbnail=\"off\" show_content=\"off\" show_more=\"off\" show_author=\"on\" show_date=\"on\" show_categories=\"off\" show_comments=\"off\" show_pagination=\"on\" offset_number=\"0\" use_overlay=\"off\" background_layout=\"light\" use_dropshadow=\"on\" use_border_color=\"on\" border_color=\"#e5e5e5\" border_style=\"solid\" \/][\/et_pb_column][\/et_pb_section]<\/p>","_et_gb_content_width":"","jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","enabled":false},"version":2},"_links_to":"","_links_to_target":""},"categories":[127,51],"tags":[],"class_list":["post-21683","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-aviation-and-astronautics","category-news"],"jetpack_publicize_connections":[],"yoast_head":"\n\n