IFR Comm Failure before Approach - NIZUS Question

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Rwy17
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IFR Comm Failure before Approach - NIZUS Question

Post by Rwy17 »

Can anyone help me understand the logic behind the question and answer? Im trying to find out if this is a mistake or not on the NIZUS Iatra practice exam.

You are radar vectored for a straight-in ILS approach in IMC. ATC cleared you to 3,000 and the MSA is 3,800. While on your final vector for the straight in ILS, you experience a two way communication failure. What should you do?

1 - Squawk Mode A/3 7600, proceed directly to the IAF at 3000 feet, hold on your inbound track until your EAT and then fly the ILS straight-in approach.

2- Squawk Mode A/3 7600, Intercept the localizer then the glide slope at 3,000 feet and then fly the ILS straight-in approach.

3- Squawk mode A/3 7600, descend to 3,000 feet and fly the ILS straight-in approach.

4- Squawk Mode A/3 7600, Intercept the localizer then the glide slope at 3,800 feet, and then fly the ILS straight in approach.

I chose (1) using this logic: You have already been cleared to 3,000 which means that 3,000 is your safe altitude since ATC is responsible for Obstacle clearance on Vectors. You have not been cleared for the approach yet so you fly to the IAF and hold until your estimated approach time that was either given or on your flight plan.

Nizus says the answer is (4). Can someone help me understand why that is?
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ReserveTank
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by ReserveTank »

Fly the highest of Minimum, Expected, or Assigned. In this case Minimum is higher.

The question did not state specifically that there was an EAT given to the aircraft from ATC, so there's no reason to hold if you're on vectors to the front course.

Also, vectored (assigned) altitudes are often lower than minimum published altitudes because you're being monitored on a scope. Once you've lost comms, you no longer have that protection anymore.

Summary: You're cleared all the way in, but must fly the publish altitudes.
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frog
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by frog »

That is a bit tricky cause ATC cleared you to 3000'.
The reason for this clearance could be that keeping 3800' til intercept would put you above the GS.
I would have gotten the wrong answer but I would have descended to 3000' intercept the loc and do the approach.
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rxl
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by rxl »

From TC AIM RAC 6.3.2.2 -

“NOTES:
1. The intent of this is that an aircraft that has experienced a
communications failure will, during any segment of a flight,
be flown at an altitude that provides the required obstacle
clearance.
2. If the failure occurs while being vectored at a radar vectoring
altitude that is lower than a published IFR altitude, the pilot
shall immediately climb to and maintain the appropriate
minimum IFR altitude until arrival at the fix, route or airway
specified in the clearance.
(iii) Descent for Approach: Maintain en route altitude to
the navigation facility or the approach fix to be used
for the IAP selected and commence an appropriate
descent procedure at whichever of the following times
is the most recent:
(A) the ETA (ETA as calculated from take-off time
plus the estimated time en route filed or amended
[with ATC]);
(A) the ETA last notified to and acknowledged by
ATC; or
(A) the EAT last received and acknowledged.
If failure occurs after you have received and acknowledged a
holding instruction, hold as directed and commence an instrument
approach at the EAT or expected further clearance time (EFC),
whichever has been issued.”

Pretty clear from this that answer 4 is correct.
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CpnCrunch
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by CpnCrunch »

frog wrote: Mon Oct 19, 2020 1:39 pm That is a bit tricky cause ATC cleared you to 3000'.
The reason for this clearance could be that keeping 3800' til intercept would put you above the GS.
I would have gotten the wrong answer but I would have descended to 3000' intercept the loc and do the approach.
Should still get a good signal at 3800 as it's less than 1 degree above GS, I believe.
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frog
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by frog »

It is a point, also I reread those answers and sure enough, #4 is the best.

However in real life, it is also a matter of common sense.

Sometimes ATC vectors you for a 7 miles final, hence in certain cases clearing you bellow the MSA.

So in this case, I won't climb back again as I would end up above the glide.
The last thing you want is an unstable approach on top of the comm failure in a busy place.
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DanWEC
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by DanWEC »

I agree, this is a good example of the correct book answer compared with what could be done a little differently in real life, depending.

The correct course of action for comm failure when being vectored below MSA is to climb to MSA and continue the approach. So, 4.

Since this is the textbook action, it's also what the controller might expect to see you do as well, and they would adjust traffic accordingly.

That being said, it would be utterly ridiculous for ATC to give you an altitude on the last final intercept vector, of which continued, would result in a CFIT on approach. Would it be "3000, but then you'll have to climb back up over that tower, the descend again". Would never happen. ATC vectoring is supposed to give 500' of mandatory clearance as well.

Let's say the 3000 was because you're brought in a bit closer, and 3800 would have you above the path, which comes with it's own set of complications. Ideally not something you want to compound a comm failure with, depending on your workload.

So in real life, depending on the circumstances, what airplane, equipment, location, all types of SA, I'd at least consider continuing the clearance at 3 if it would seem to be the safest option for all involved in that specific situation, but the book answer is definitely to climb, and the golden rule is "When in doubt" (And make sure you can make a good case to defend yourself to the CP as well!)
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Big Pistons Forever
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by Big Pistons Forever »

If I am answering the exam question I would climb to 3800, if I was actually flying this profile I would descend to 3000, intercept the Loc and GS and then land, for all the reasons DANWEC presented
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Donald
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by Donald »

In real life, how would you know you've had a comm failure?

You've been given the heading and altitude to intercept the localizer, the next instruction you are expecting is to switch to tower/mandatory frequency.

In the real world, you would intercept the localizer at 3,000 and await instruction to switch frequencies. By the time you realize that there is a comm failure, you'd already be on the approach.
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frog
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by frog »

Yes and no !

You've been given the clearance to descend to 3000' and intercept on present heading and clear for the approach...and then comm failure !
So ATC calls you back for acknowledgement, you can hear ATC but you can't transmit ! :)

I know it is far fetched !
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Big Pistons Forever
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by Big Pistons Forever »

frog wrote: Tue Oct 20, 2020 9:28 am Yes and no !

You've been given the clearance to descend to 3000' and intercept on present heading and clear for the approach...and then comm failure !
So ATC calls you back for acknowledgement, you can hear ATC but you can't transmit ! :)

I know it is far fetched !
When ATC sees you sqawking 7600 and the aircraft descending towards 3000 they are going to know you have got the last clearance. They are going to tell tower you are NORDO and you are going to intercept the ILS and go ahead and land. Simples...
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frog
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by frog »

:)

Good point !
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455tt
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by 455tt »

What reference(s) is/are provided by the authors for this particular question?

Most exam prep's will have some kind of reference system so the user can source the background material for their questions. It enhances the authority of their product.

Or is this not the case with NIZUS, and they just display their questions only, for you to do the background research on your own.
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Donald
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by Donald »

frog wrote: Tue Oct 20, 2020 9:28 am Yes and no !

You've been given the clearance to descend to 3000' and intercept on present heading and clear for the approach...and then comm failure !
So ATC calls you back for acknowledgement, you can hear ATC but you can't transmit ! :)

I know it is far fetched !
“While on your final vector, you experience a two-way comm failure.”

2-ways, I assume, means your radio goes silent and you don’t hear anything.

I still say, as per the situation described, in the real world you would just keep trucking on the approach and wouldn’t recognize the comm failure until after you were established.

Just splitting hairs on the semantics of a hypothetical exam question of course.
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Hotoffthepress
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by Hotoffthepress »

This is a typical scenario that happens many times for Check Rides in the Simulator. Trick is to only descend as per procedure.

I find it helps when being questioned about IFR is to always assume you're not visual. In this particular case, "radar vectored for a straight-in ILS approach in IMC". You cannot see the terrain as you are in IMC. When being radar vectored, consider yourself "off the path", meaning you're deviating from the procedure approach which is approved by ATC (Normally for shortcuts).

ATC clears you to 3,000 and the MSA is 3,800. ATC in this case is responsible for terrain clearance via radar vectors, and they clear you to descent below Minimum Safe Altitude of 3800. No problems here.

"While on your final vector for the straight in ILS, you experience a two way communication failure"
Because you have lost contact with ATC and you're currently "off the path", you are now responsible for Terrain Clearance. The problem is that you cannot see the terrain as you're in IMC, and the MSA is 3800.

To stay safe, you must maintain MSA 3800 to clear terrain to maintain your current "off the path" vector to intercept the Localiser. Then intercept the Localiser. Only when established on the localiser which grants you terrain clearance, can you intercept the glideslope.

I hope this answers it.

Real life, airmanship takes precedence.
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TeePeeCreeper
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by TeePeeCreeper »

Hotoffthepress wrote: Wed Oct 13, 2021 12:24 am This is a typical scenario that happens many times for Check Rides in the Simulator. Trick is to only descend as per procedure.

I find it helps when being questioned about IFR is to always assume you're not visual. In this particular case, "radar vectored for a straight-in ILS approach in IMC". You cannot see the terrain as you are in IMC. When being radar vectored, consider yourself "off the path", meaning you're deviating from the procedure approach which is approved by ATC (Normally for shortcuts).

ATC clears you to 3,000 and the MSA is 3,800. ATC in this case is responsible for terrain clearance via radar vectors, and they clear you to descent below Minimum Safe Altitude of 3800. No problems here.

"While on your final vector for the straight in ILS, you experience a two way communication failure"
Because you have lost contact with ATC and you're currently "off the path", you are now responsible for Terrain Clearance. The problem is that you cannot see the terrain as you're in IMC, and the MSA is 3800.

To stay safe, you must maintain MSA 3800 to clear terrain to maintain your current "off the path" vector to intercept the Localiser. Then intercept the Localiser. Only when established on the localiser which grants you terrain clearance, can you intercept the glideslope.

I hope this answers it.

Real life, airmanship takes precedence.
Good write up, but not so “hot off the press” almost a year later and after the horse had been beaten around the LOC to a pulp! :D
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Hotoffthepress
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Re: IFR Comm Failure before Approach - NIZUS Question

Post by Hotoffthepress »

:D

Cold off the press
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