787 IRS on during turnaround- engineering requirement?
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787 IRS on during turnaround- engineering requirement?
One engineer recently told me that they prefer us to leave the the IRS on as it facilitates wireless communication of engineering data between the aircraft and the centre of the maintenance universe?
Our shutdown checklist say they should be off. Our Flight Crew Operating Manual says "As required". Spoken to four Monarch engineers none of whom could suggest a good reason for leaving the IRS on?
Any thoughts..thanks in advance!
Our shutdown checklist say they should be off. Our Flight Crew Operating Manual says "As required". Spoken to four Monarch engineers none of whom could suggest a good reason for leaving the IRS on?
Any thoughts..thanks in advance!
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I can't speak for the 787 only the other plastic jet the A350, the first thing I do on entering the flt deck is put the ADIRU's on, this allows, EFB comms with the ground, it allows IFE to be functioning and checked, it allows fuelling to be carried out plus a few other things as they all need ADIRU inputs, I can only guess that it may be somewhat similar on the 787, I could of course be totally wrong.
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RMC
Speaking of experience I had on the 767, all the time I put the IRS to OFF after the shutdown check-list, I get a NO COMM message on the ACARS/DATALINK screen.
I guess the datalink, especially the satcom module, needs to know where the aircraft is sitting in order to auto-tune the right sat channel (and probably also the VHF ACARS, as the frequency changes according to the region you are located).
Never made an in-depth research on this, though.
BF
Speaking of experience I had on the 767, all the time I put the IRS to OFF after the shutdown check-list, I get a NO COMM message on the ACARS/DATALINK screen.
I guess the datalink, especially the satcom module, needs to know where the aircraft is sitting in order to auto-tune the right sat channel (and probably also the VHF ACARS, as the frequency changes according to the region you are located).
Never made an in-depth research on this, though.
BF
Must admit having been brought watching traditional navigators baby sitting the early inertial systems to get a working alignment and done a bit of the same on a classic airframe the “I’d aligned it up for you, why have you recycled it?” comment is one of my pet peeves.....(though I know people are well meaning and have their reasons...)
I can’t talk for the 787 but on traditional types there is/was often a maximum time limitation between full inertial system aligns (to prevent accrual of errors) and also a requirement for the operating crew, not the engineer, to enter/ensure the correct PPos is entered at the start of the alignment process.....
AFAIK the only way crew could ensure both of the above was to turn the system off and on again as part of the shutdown and/or preflight procedure....which is possibly whilst it might still be in a checklist.. Whether there really is any reason these days for such precautions I don’t know....and yes, nowadays there’s the added issue of loss of satcom whilst the system is off or aligning....
Ultimately you follow the checklist...but yes I am old fashioned.....
I can’t talk for the 787 but on traditional types there is/was often a maximum time limitation between full inertial system aligns (to prevent accrual of errors) and also a requirement for the operating crew, not the engineer, to enter/ensure the correct PPos is entered at the start of the alignment process.....
AFAIK the only way crew could ensure both of the above was to turn the system off and on again as part of the shutdown and/or preflight procedure....which is possibly whilst it might still be in a checklist.. Whether there really is any reason these days for such precautions I don’t know....and yes, nowadays there’s the added issue of loss of satcom whilst the system is off or aligning....
Ultimately you follow the checklist...but yes I am old fashioned.....
787.
The reason I turn the IRS on is to clear the multitude of EICAS Status messages from the screen. Too much clutter makes it hard to see if there is a new snag.
In addition if there is an in-bound defect in the log book or one appears out of nowhere between crew exit and me entering then, half the time, you may need the IRS aligned anyway to troubleshoot the fault.
The reason I turn the IRS on is to clear the multitude of EICAS Status messages from the screen. Too much clutter makes it hard to see if there is a new snag.
In addition if there is an in-bound defect in the log book or one appears out of nowhere between crew exit and me entering then, half the time, you may need the IRS aligned anyway to troubleshoot the fault.
If the aircraft is using an Inmarsat SATCOM datalink for transmitting engineering data to company maintenance operations, the IRUs need to be on and aligned. This is necessary in order for the steerable SATCOM antenna to find and lock on to the appropriate geostationary satellite for the aircraft’s current location. GPS coordinates alone are not sufficient- the antenna controller needs to know the aircraft’s current pitch/roll/yaw orientation - (in particular, its heading) - to find the proper satellite. That information can only come from the IRU/ADIRU.
I think most pilots understand all the above re satcom and fault finding etc..but from a "drivers" POV regardless of what the engineers need/want there is still the issue of whether a "fresh" align is need for every turn, which takes us back to what the OP's company SOPs/FCOM say on the matter.
For the sake of any engineers contributing whilst I can't speak for our company's 787 procedures FWIW on 744 and 777 at least to ensure a best case align/best nav accuracy we have a requirement in our SOPs to re-align the IRS on every preflight, and a requirement to ensure we, i.e the flight crew, enter the present position prior to that align. That means turn the IRS(s) off and then back on again, even if the ground engineer says he/she has just done the necessary just before we got on board...it does sometimes raise comments or an eyebrow..it's nothing personal, it's not a case of not trusting the ground engineers, but in the case of some bizarre nav problem post launch I think most of us would be like to be able to say we'd stuck with the company procedures..
For the sake of any engineers contributing whilst I can't speak for our company's 787 procedures FWIW on 744 and 777 at least to ensure a best case align/best nav accuracy we have a requirement in our SOPs to re-align the IRS on every preflight, and a requirement to ensure we, i.e the flight crew, enter the present position prior to that align. That means turn the IRS(s) off and then back on again, even if the ground engineer says he/she has just done the necessary just before we got on board...it does sometimes raise comments or an eyebrow..it's nothing personal, it's not a case of not trusting the ground engineers, but in the case of some bizarre nav problem post launch I think most of us would be like to be able to say we'd stuck with the company procedures..
Last edited by wiggy; 30th Dec 2017 at 08:54.
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I think most pilots understand all the above re satcom and fault finding etc..but from a "drivers" POV regardless of what the engineers need/want there is still the issue of whether a "fresh" align is need for every turn, which takes us back to what the OP's company SOPs/FCOM say on the matter.
For the sake of any engineers contributing whilst I can't speak for our company's 787 procedures FWIW on 744 and 777 at least to ensure a best case align/best nav accuracy we have a requirement in our SOPs to re-align the IRS on every preflight, and a requirement to ensure we, i.e the flight crew, enter the present position prior to that align. That means turn the IRS(s) off and then back on again, even if the ground engineer says he/she has just done the necessary just before we got on board...it does sometimes raise comments or an eyebrow..it's nothing personal, it's not a case of not trusting the ground engineers, but in the case of some bizarre nav problem post launch I think most of us would be like to be able to say we'd stuck with the company procedures..
For the sake of any engineers contributing whilst I can't speak for our company's 787 procedures FWIW on 744 and 777 at least to ensure a best case align/best nav accuracy we have a requirement in our SOPs to re-align the IRS on every preflight, and a requirement to ensure we, i.e the flight crew, enter the present position prior to that align. That means turn the IRS(s) off and then back on again, even if the ground engineer says he/she has just done the necessary just before we got on board...it does sometimes raise comments or an eyebrow..it's nothing personal, it's not a case of not trusting the ground engineers, but in the case of some bizarre nav problem post launch I think most of us would be like to be able to say we'd stuck with the company procedures..
However please ensure you check first, I was in the middle of a 10 minute test the other day that required the ADIRU's on, crew got on and immediately switched them off, behind my back, even though I was in the left seat doing what I had to do, didn't even ask, suffice to say he won't do it again!
