tag:blogger.com,1999:blog-3991004594884305625.post924062707693726085..comments2023-11-28T23:42:25.873-08:00Comments on Satcom Guru: Sriwijaya Air flight SJ182Peter Lemmehttp://www.blogger.com/profile/16409315777756590084noreply@blogger.comBlogger9125tag:blogger.com,1999:blog-3991004594884305625.post-34228236432486456742021-02-02T11:13:33.466-08:002021-02-02T11:13:33.466-08:00I wonder if unreliable airspeed could have lead to...I wonder if unreliable airspeed could have lead to a stall with subsequent panic and loss of control. Weather condition did not seem to be unusual. I recall the 1998? BirgenAir 757 accident caused by a single plugged pitot.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3991004594884305625.post-59427755630935569212021-01-12T10:16:38.443-08:002021-01-12T10:16:38.443-08:00I'd have said, based on the FR24 data, that Ro...I'd have said, based on the FR24 data, that RoD was more-or-less constant from about 8000 ft until impact.<br /><br />That said, horizontal speed increased towards the end of the dive (from around 4000 feet, 5 seconds before impact), implying that the aircraft was pulling out.<br /><br />I'd be interested to see your calculations of FPA vs time and vs altitude.Davehttps://www.blogger.com/profile/03508264279995565243noreply@blogger.comtag:blogger.com,1999:blog-3991004594884305625.post-90758332533018992882021-01-11T15:33:03.783-08:002021-01-11T15:33:03.783-08:00the altitude trace is not a straight line. It most...the altitude trace is not a straight line. It most closely matches a second-order polynomial. The plots I shared operate off of a moving window difference calculation on the raw data, so they are noisy. If you model the altitude by curve-fit, the difference calculation (vertical speed) smooths out. In either case, vertical speed *increased throughout the descent*. It does look like at around 10-12 seconds from the end, the flight path began to "inflect", or started to shallow out a little bit - the beginning of a pullout. Peter Lemmehttps://www.blogger.com/profile/16409315777756590084noreply@blogger.comtag:blogger.com,1999:blog-3991004594884305625.post-79811918812764647552021-01-11T15:05:49.242-08:002021-01-11T15:05:49.242-08:00Appreciate the spelling correction.
I did mean m...Appreciate the spelling correction. <br /><br />I did mean minimum, in that Vd must be at least 1.25 Vmo or sufficient for a specified pull up maneuver. It is possible to be less than the 25% margin I quoted - I will note that more clearly. <br /><br />Reportedly, the debris pattern matches most closely to breaking up upon impacting with the sea, which makes the dive speed less an issue.<br /><br />ET302 approached 500 knots airspeed. <br /><br />Here is the verbiage from 25.335<br /><br />§ 25.335 Design airspeeds.<br />The selected design airspeeds are equivalent airspeeds (EAS). Estimated values of VS0 and VS1 must be conservative.<br />(a) Design cruising speed, VC. For VC, the following apply:<br />(1) The minimum value of VC must be sufficiently greater than VB to provide for inadvertent speed increases likely to occur as a result of severe atmospheric turbulence.<br />(2) Except as provided in §25.335(d)(2), VC may not be less than VB + 1.32 UREF (with UREF as specified in §25.341(a)(5)(i)). However VC need not exceed the maximum speed in level flight at maximum continuous power for the corresponding altitude.<br />(3) At altitudes where VD is limited by Mach number, VC may be limited to a selected Mach number.<br />(b) Design dive speed, VD. VD must be selected so that VC/MC is not greater than 0.8 VD/MD, or so that the min- imum speed margin between VC/MC and VD/MD is the greater of the following values:<br />(1) From an initial condition of sta- bilized flight at VC/MC, the airplane is upset, flown for 20 seconds along a flight path 7.5° below the initial path, and then pulled up at a load factor of 1.5g (0.5g acceleration increment). The speed increase occurring in this maneu- ver may be calculated if reliable or conservative aerodynamic data is used. Power as specified in §25.175(b)(1)(iv) is assumed until the pullup is initiated, at which time power reduction and the use of pilot controlled drag devices may be assumed;<br />(2) The minimum speed margin must be enough to provide for atmospheric variations (such as horizontal gusts, and penetration of jet streams and cold fronts) and for instrument errors and airframe production variations. These factors may be considered on a probability basis. The margin at altitude where MC is limited by compressibility effects must not less than 0.07M unless a lower margin is determined using a rational analysis that includes the effects of any automatic systems. In anyPeter Lemmehttps://www.blogger.com/profile/16409315777756590084noreply@blogger.comtag:blogger.com,1999:blog-3991004594884305625.post-46761365721576358312021-01-11T12:36:32.044-08:002021-01-11T12:36:32.044-08:00Two nitpicky things:
"3D speed difference cal...Two nitpicky things:<br />"3D speed difference calculation is course and thus has significant variation. It should be noted how closely the 3D speed follows ground speed prior to the upset event, giving confidence the calculation is representative. "<br />I think you mean "coarse", not "course"<br />" The final 3D speed of about 435 knots does not appear to exceed the minimum dive speed (Vmo 340 times 1.25) of 425 knots by much",<br />I think you mean "maximum", not "minimum".<br />Great write up!!<br /><br />Anonymoushttps://www.blogger.com/profile/06100113308705763805noreply@blogger.comtag:blogger.com,1999:blog-3991004594884305625.post-43635435759139322012021-01-11T03:34:25.980-08:002021-01-11T03:34:25.980-08:00A question. During the last 15 seconds your (press...A question. During the last 15 seconds your (pressure) altitude plot shows a roughly linear progression (a straight line). All good so far. Given that vertical speed is a function of change in that altitude with time, how do you get an increasing vertical speed with time in that period? The vertical speed during that last 15 seconds is roughly constant surely?Stevehttps://www.blogger.com/profile/02978205578300048409noreply@blogger.comtag:blogger.com,1999:blog-3991004594884305625.post-7046649469477974572021-01-11T00:16:51.343-08:002021-01-11T00:16:51.343-08:00I put caveats around the discussion to avoid any a...I put caveats around the discussion to avoid any assertion that a rudder event happened on SJ182 without additional proof. My stated point is that the accident investigation needs to determine whether a rudder malfunction was a contributing factor. It would be very disappointing to have another rudder event.Peter Lemmehttps://www.blogger.com/profile/16409315777756590084noreply@blogger.comtag:blogger.com,1999:blog-3991004594884305625.post-23323582243738891072021-01-11T00:02:05.648-08:002021-01-11T00:02:05.648-08:00Although not mentioned here, there was a great dea...Although not mentioned here, there was a great deal of work done on the 737 rudder systems, long after the initial valve issue was identified and resolved. There has never been another rudder event since that work was done. So it is far too soon to speculate about rudder issues. Right now, the possibility of rudder malfunction is no more or less likely than any other cause.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3991004594884305625.post-89335483118312815292021-01-10T14:11:46.729-08:002021-01-10T14:11:46.729-08:00Peter, wonderful work as usual, thank you.
Jeff W...Peter, wonderful work as usual, thank you. <br />Jeff WiseAnonymousnoreply@blogger.com