B737-700 captain reported a momentary lost of flight path guidance while conducting an ILS approach ...

Narrative:

While conducting the CAT ii sa xxl into ZZZ we experienced momentary flight path symbol and flight guidance cue (aiii mode) movement due to an aircraft departing on our runway as we were inside a five-mile final. This was obviously distracting while conducting an approach to a runway with a reported RVR of 1; 600 feet (I believe). My question is; why was the ILS critical area not protected? It is my understanding that if the weather is less than 800 and/or two miles visibility; this area should be protected while aircraft are inside the OM or the fix used in lieu of. We have another question regarding protection of the ILS critical area in ZZZ1. We were operating flight XXXX; ZZZ1-ZZZ2. ZZZ1 weather was reported as 200 broken 1/4 mile visibility. We called ground control for taxi. 'Taxi runway xx via U and west; report turning on to west.' there was no mention of 'hold short of the ILS critical area.' again; why not? If ATC does not specifically state a 'hold short' clearance then we are cleared to the runway hold short markings. My reason for submitting this [report] is to help me and possibly others understand the purpose of the ILS critical area. In advance; thank you for providing more clarity on this issue.

Original NASA ASRS Text

Title: B737-700 Captain reported a momentary lost of flight path guidance while conducting an ILS approach at the same time a flight was departing from the approach runway.

Narrative: While conducting the CAT II SA XXL into ZZZ we experienced momentary Flight Path symbol and Flight Guidance Cue (AIII mode) movement due to an aircraft departing on our runway as we were inside a five-mile final. This was obviously distracting while conducting an approach to a runway with a reported RVR of 1; 600 feet (I believe). My question is; why was the ILS Critical area not protected? It is my understanding that if the weather is less than 800 and/or two miles visibility; this area should be protected while aircraft are inside the OM or the fix used in lieu of. We have another question regarding protection of the ILS Critical area in ZZZ1. We were operating Flight XXXX; ZZZ1-ZZZ2. ZZZ1 weather was reported as 200 broken 1/4 mile visibility. We called Ground Control for taxi. 'Taxi Runway XX via U and W; report turning on to W.' There was no mention of 'hold short of the ILS Critical area.' Again; why not? If ATC does not specifically state a 'hold short' clearance then we are cleared to the runway hold short markings. My reason for submitting this [report] is to help me and possibly others understand the purpose of the ILS Critical Area. In advance; thank you for providing more clarity on this issue.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1721778
Time
Date	202001
Place
Locale Reference	ZZZ.Airport
State Reference	US
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Component
Aircraft Component	ILS/VOR
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Instrument Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 458
Events
Anomaly	ATC Issue All Types Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy

B737-700 captain reported a momentary lost of flight path guidance while conducting an ILS approach at the same time a flight was departing from the approach runway.