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ATPL interview

Asked by: 3592 views Instrument Rating

Dear sir,

              i am CPL holder, from India. i am preparing for  my ATPL interview. i have few doubts for which i cant find the answer or the relevent information, if the questions are silly kindly forgive me for my ignorance.

Questions are as follows,

1. Why does the minimu increase incase of Approach light fails?

2. what is the glide slope failure warning in the cockpit, and how can we determine whether it is a transmitter or receiver failure?

3. During ILS approach, if DME and OM/MM/IM fails, can we continue the approach?

THanking you,



3 Answers

  1. Best Answer

    John D. Collins on Dec 27, 2011

    1. The visibility minimums are usually increased when the approach light system is out of service because without them working, it is impossible to see the runway at the lowest minimums of 200-1/2 and without the lights, there is no way to complete the approach unless the visibility is increased.  Assume the visibility is actually 1/2 statute mile or half of 5280 = 2640 feet.  At a DH of 200 feet, you are still 3821 feet from the touchdown point and 2861 feet from the threshold (GS angle 3 degrees and a TCH of 40 feet). Adding a 1/4 mile to the visibility requirement, will give you 3960 feet of forward visibility.  With the lights working, you are allowed to continue the descent to 100 feet above the runway, solely on the basis of the lights. At 100 feet, you need one of the other indications, such as the runway threshold lights to continue the approach and you will only be 1911 feet from the touchdown point and 957 feet from the threshold.

    2.  Depending on the HSI or CDI you are using, they have a flag that indicates the GS is not working.  Some HSI’s such as the KCS55A system, will retract the GS indicators out of view when the GS is not valid.  There are failure conditions where the GS flag does not show, but the system is not operating. I had this happen to me on one ILS approach and it was caused by the avionics not being properly seated.  I have heard of a case where a valid GS might be generated without a flag during maintenance of the ground system.  Cross checking the altitude at the FAF will help identify this kind of condition.  I don’t know of any foolproof way of determining if the GS failed or the avionics failed.

    3. This depends on the approach.  For a full ILS, once you intercept the GS, the DME or markers are not used to determine the MAP, it is determined by being at the DH and on the GS.  However, the DME may be required for the missed approach.  A localizer approach may require a DME and if it doesn’t have a timing table, there is no other way of determining any step downs or the MAP.  For the most part, marker beacons are being removed from approaches as they are not deemed necessary, particularly the OM.

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  2. srishan on Dec 29, 2011

    thanks for your reply

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  3. srishan on Jan 04, 2012

     What is the difference between pans-ops 3 and pans-ops 4 ?

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