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#11
Hangar 7 / Re: CF6 ECU ALTN
Last post by John H Watson - Thu, 30 Mar 2023 13:18Quote from: ASCTU744 on Thu, 30 Mar 2023 10:41So only a loss of PT2 (ADC) results in a change of reversionary mode. When the TAT data is lost, the ECU uses T12.
When PT2 is lost and the transition occurs, the ECU chooses not to use T12 data. But instead the last valid ADC data is used. (Why?)
T12 is temperature. PT2 is "total air pressure". i.e. pitot pressure with temperature compensation
Quote from: Hardy Heinlin on Thu, 30 Mar 2023 11:46"The normal control mode is used if PT2 LADC and PT2 RADC are both available and valid, and agree within 0.437 psia. Probe heat must also be ON. If these conditions are not met, the EEC automatically enters a soft reversionary control mode."
Despite the agreement check, this text says that the soft reversionary mode even occurs when just either PT2 alone is unavailable.
This now seems to make more sense. Total pressure seems to be rather critical. It must be compared with something to confirm its accuracy (L and R ADC values) and the engine cannot provide an equivalent. There is no inlet pressure sensor (unlike the RB211 which has a P2T2 probe)
#12
Hangar 7 / Re: CF6 ECU ALTN
Last post by Hardy Heinlin - Thu, 30 Mar 2023 11:46That 5 sec delay per se may be correct. There are further, general delays in the system until the message actually appears on the screen, and the total time may be 10 sec then. So that SSM doesn't necessarily disagree with my quoted text.
I'm now refreshing that part in my brain which stored the EEC stuff 12 years ago. A long time. OK, one more thing. My afore-mentioned "delta" is not a delta between sensors but simply the delta between sensor and ISA:
"The selected PT2 value is used with the difference between ambient and standard day temperature (DTAMB), and the ambient temperature (TAMB) to calculate mach number (Mn) and impact pressure (Q)."
Nevertheless, there is a disagreement check:
"The normal control mode is used if PT2 LADC and PT2 RADC are both available and valid, and agree within 0.437 psia. Probe heat must also be ON. If these conditions are not met, the EEC automatically enters a soft reversionary control mode."
Despite the agreement check, this text says that the soft reversionary mode even occurs when just either PT2 alone is unavailable. That's at least my understanding when I look at logical operators like a programmer. So when a single ADC L or R fails, and, if installed, ADC C fails as well, then both PT2 are simply no longer available.
IF PT2_LADC_avail_valid_heated AND PT2_RADC_avail_valid_heated
THEN Normal_mode
ELSE Soft_rev_mode
This also agrees with the text I quoted in my previous comment.
The EEC knows the last stored DTAMB (ISA OAT deviation). So when the engine's T12 sensor indicates temp changes, the EEC also can -- based on that DTAMB -- calculate the corresponding changes in the pressure altitude. Of course, this isn't exact. It's just an assumption.
I'm wondering what happens when the changing temp from T12 isn't caused by an altitude change but by an airspeed change. The EEC might interprete an increasing airspeed as a decreasing altitude, and vice versa. This whole stuff is probably intended for the mode change only, so that there are no thrust changes in the moment of the mode change.
There are two DTAMB values. One for the soft, one for the hard reversionary mode. The latter is the "cornerpoint" DTAMB; that's greater than the other one for the soft mode. Therefore it may cause overboosting. I'm not sure why the designers added that greater "cornerpoint" DTAMB. Maybe it assures that all engines get the same reference instead of using individual last stored DTAMB values. This may also be the reason the CF6 can keep using the autothrottle when all EECs are in hard reversionary mode (which is impossible on RR and PW).
Another confusing thing regarding the hard reversionary mode:
"The cornerpoint DTAMB value is used to calculate an assumed TAMB as altitude changes, and to calculate Mn and Q."
How can the hard reversionary mode know the altitude when the EEC has just a cornerpoint DTAMB and its own temp sensors? (No ADC data.) Does this text mean to say that the hard mode will calculate an assumed altitude (like in soft mode), and by that assumed altitude it will calculate an assumed TAMB? (Which is then used to calculate Mach number and impact pressure.)
I'm now refreshing that part in my brain which stored the EEC stuff 12 years ago. A long time. OK, one more thing. My afore-mentioned "delta" is not a delta between sensors but simply the delta between sensor and ISA:
"The selected PT2 value is used with the difference between ambient and standard day temperature (DTAMB), and the ambient temperature (TAMB) to calculate mach number (Mn) and impact pressure (Q)."
Nevertheless, there is a disagreement check:
"The normal control mode is used if PT2 LADC and PT2 RADC are both available and valid, and agree within 0.437 psia. Probe heat must also be ON. If these conditions are not met, the EEC automatically enters a soft reversionary control mode."
Despite the agreement check, this text says that the soft reversionary mode even occurs when just either PT2 alone is unavailable. That's at least my understanding when I look at logical operators like a programmer. So when a single ADC L or R fails, and, if installed, ADC C fails as well, then both PT2 are simply no longer available.
IF PT2_LADC_avail_valid_heated AND PT2_RADC_avail_valid_heated
THEN Normal_mode
ELSE Soft_rev_mode
This also agrees with the text I quoted in my previous comment.
The EEC knows the last stored DTAMB (ISA OAT deviation). So when the engine's T12 sensor indicates temp changes, the EEC also can -- based on that DTAMB -- calculate the corresponding changes in the pressure altitude. Of course, this isn't exact. It's just an assumption.
I'm wondering what happens when the changing temp from T12 isn't caused by an altitude change but by an airspeed change. The EEC might interprete an increasing airspeed as a decreasing altitude, and vice versa. This whole stuff is probably intended for the mode change only, so that there are no thrust changes in the moment of the mode change.
There are two DTAMB values. One for the soft, one for the hard reversionary mode. The latter is the "cornerpoint" DTAMB; that's greater than the other one for the soft mode. Therefore it may cause overboosting. I'm not sure why the designers added that greater "cornerpoint" DTAMB. Maybe it assures that all engines get the same reference instead of using individual last stored DTAMB values. This may also be the reason the CF6 can keep using the autothrottle when all EECs are in hard reversionary mode (which is impossible on RR and PW).
Another confusing thing regarding the hard reversionary mode:
"The cornerpoint DTAMB value is used to calculate an assumed TAMB as altitude changes, and to calculate Mn and Q."
How can the hard reversionary mode know the altitude when the EEC has just a cornerpoint DTAMB and its own temp sensors? (No ADC data.) Does this text mean to say that the hard mode will calculate an assumed altitude (like in soft mode), and by that assumed altitude it will calculate an assumed TAMB? (Which is then used to calculate Mach number and impact pressure.)
#13
Hangar 7 / Re: CF6 ECU ALTN
Last post by ASCTU744 - Thu, 30 Mar 2023 11:15My china airlines SSM says 5 sec, but probably an airline option. Thx!
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#14
Hangar 7 / Re: CF6 ECU ALTN
Last post by Hardy Heinlin - Thu, 30 Mar 2023 11:07Well, OK, the "other" CF6 book says this:
"If the EEC fails to receive a valid total pressure value from either ADC or probe heat fails, the EEC operates in a soft reversionary control mode. If N2 is greater than 50 percent, as sensed by the N2 speed card, the ALTN light in the EEC control switch comes on after 10 seconds and the EICAS level C message ENG X EEC MODE appears. This message is also latched as an EICAS status message."
I'll modify that for the CF6 model in the next PSX update.
|-|
"If the EEC fails to receive a valid total pressure value from either ADC or probe heat fails, the EEC operates in a soft reversionary control mode. If N2 is greater than 50 percent, as sensed by the N2 speed card, the ALTN light in the EEC control switch comes on after 10 seconds and the EICAS level C message ENG X EEC MODE appears. This message is also latched as an EICAS status message."
I'll modify that for the CF6 model in the next PSX update.
|-|
#15
Hangar 7 / Re: CF6 ECU ALTN
Last post by ASCTU744 - Thu, 30 Mar 2023 10:41Just a quick recap:
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So only a loss of PT2 (ADC) results in a change of reversionary mode. When the TAT data is lost, the ECU uses T12.
When PT2 is lost and the transition occurs, the ECU chooses not to use T12 data. But instead the last valid ADC data is used. (Why?)
Note: This is all from KLM
So only a loss of PT2 (ADC) results in a change of reversionary mode. When the TAT data is lost, the ECU uses T12.
When PT2 is lost and the transition occurs, the ECU chooses not to use T12 data. But instead the last valid ADC data is used. (Why?)
Note: This is all from KLM
#16
Hangar 7 / Lufthansa ditching older wide ...
Last post by cagarini - Thu, 30 Mar 2023 09:57 #17
Hangar 7 / Re: FPPM: Improved climb + Tir...
Last post by dhob - Thu, 30 Mar 2023 08:35That is interesting. The following is from Boeing's JTPM document:
When Limited by Tire Speeds
When your takeoff weight will be limited by field length, or climb, or obstacles, there exist a number of performance options that may help to increase the limit weight: improved climb, a different flap setting, air conditioning bleeds off, range of V1, and the like.
When your takeoff weight is limited by tire speeds, however, there is relatively little you can do to seek relief from this restriction. Operationally, the only options available will be to try a larger flap setting to decrease the liftoff speeds, or to schedule the flights for cooler times of day.
Logically, no increase in V Speeds would be possible if at tire speed weight limit. I agree the FPPM chart doesn't seem to have any applicability.
When Limited by Tire Speeds
When your takeoff weight will be limited by field length, or climb, or obstacles, there exist a number of performance options that may help to increase the limit weight: improved climb, a different flap setting, air conditioning bleeds off, range of V1, and the like.
When your takeoff weight is limited by tire speeds, however, there is relatively little you can do to seek relief from this restriction. Operationally, the only options available will be to try a larger flap setting to decrease the liftoff speeds, or to schedule the flights for cooler times of day.
Logically, no increase in V Speeds would be possible if at tire speed weight limit. I agree the FPPM chart doesn't seem to have any applicability.
#18
Hangar 7 / Re: CF6 ECU ALTN
Last post by John H Watson - Thu, 30 Mar 2023 05:45Each EEC receives air data from the L and R ADC on databusses via ADC switching relays. Selecting the C ADC replaces one of the two ADCs.
L (or C) ADC data is sent to Channel A of the EEC
R (or C) ADC data is sent to Channel B of the EEC
Generally....
However, I don't understand this:
Does this mean that EEC Channel "A" PT2 data won't be sourced from Channel B? Why wouldn't the healthy Channel take over completely? Note that T12, P0, N1, N2, P3 & T25 are engine-mounted sensors.
PT2 = "total pressure"
The GE tries to determine which is the healthiest channel and selects that. I don't know if "healthy" means the internals of the EEC alone or also "unhealthy" data from external sources.
Note that all of this is taken from the GE books. The RB211 and maybe the PW will be completely different.
L (or C) ADC data is sent to Channel A of the EEC
R (or C) ADC data is sent to Channel B of the EEC
Generally....
QuoteIf an input signal is determined to be faulty or missing, the
EEC is generally able to use the input from the opposite [EEC]channel.
However, I don't understand this:
QuoteADC - TAT, P (AMBIENT).. USE ENGINE SENSORS
ADC - PT2............... SWITCH TO REVERSIONARY MODE
T12, P0................. USE CROSS CHANNEL DATA. IF BOTH SENSORS FAIL, USE LAST KNOWN DATA
N1, N2, P3, T25......... USE CROSS CHANNEL DATA. IF SENSORS DISAGREE, USE CLOSEST TO CALCULATED VALUE. BOTH SENSORS FAIL, USE CALCULATED VALUE
Does this mean that EEC Channel "A" PT2 data won't be sourced from Channel B? Why wouldn't the healthy Channel take over completely? Note that T12, P0, N1, N2, P3 & T25 are engine-mounted sensors.
PT2 = "total pressure"
The GE tries to determine which is the healthiest channel and selects that. I don't know if "healthy" means the internals of the EEC alone or also "unhealthy" data from external sources.
QuoteLOSS OF BOTH EEC CHANNELS: DRIVERS (EHSV, SOLENOID)... SWITCH TO FAILSAFE FOR ALL FUNCTIONS, EHSV TO NULL BIAS, ENGINE SHUTDOWN
Note that all of this is taken from the GE books. The RB211 and maybe the PW will be completely different.
#19
Hangar 7 / Re: CF6 ECU ALTN
Last post by Hardy Heinlin - Thu, 30 Mar 2023 01:14That includes a "Last Delta T AMB" link from the normal control box. I consider that a difference check (disagreement).
Now where does the "PT2 INPUT FAIL" signal line on this (simplified) flow chart really come from?
Now where does the "PT2 INPUT FAIL" signal line on this (simplified) flow chart really come from?
#20
Hangar 7 / Re: CF6 ECU ALTN
Last post by John H Watson - Thu, 30 Mar 2023 00:51Here's another version of that flow chart
The L/R ADC input may be dependent on ISSM switch selections.
Interestingly, with loss of "total pressure" from the ADC, the ALTN light is illuminated by the EEC sending a signal to the N2 Speed Card which illuminates the ALTN light.
Still looking for the data selection flow chart...
The L/R ADC input may be dependent on ISSM switch selections.
Interestingly, with loss of "total pressure" from the ADC, the ALTN light is illuminated by the EEC sending a signal to the N2 Speed Card which illuminates the ALTN light.
Still looking for the data selection flow chart...