B737 first officer reported a glideslope anomaly on the ILS to runway 30 at mia apparently caused by...

Narrative:

ILS to runway 30 miami. Weather was 900 foot ceiling with 3 miles vis. Two 747s were holding short of runway 12/30 on taxiway T and on runway 09 (both were pointed east waiting to cross runway 30; preparing to depart on runway 27). As we passed 800 ft on the glideslope for runway 30 with the runway in sight (100 ft below the ceiling) and the autopilot off; the glideslope began to dive for the ground. The glideslope interference was occurring from the two jumbo aircraft holding short of runway 30. We reported the interference to tower immediately. The jet behind us shortly reported the same anomaly after we landed. Had an autopilot been engaged; the aircraft would have commenced a dangerous dive beneath that PAPI visual path or ILS glideslope toward the ground. Glideslope interference from two large aircraft holding abeam the landing runway. Do not allow jumbo aircraft to hold short of runway 30 when instrument condition are less than VFR conditions.

Original NASA ASRS Text

Title: B737 First Officer reported a glideslope anomaly on the ILS to Runway 30 at MIA apparently caused by B747 aircraft holding on the taxiway in the vicinity of the end of the runway.

Narrative: ILS to Runway 30 Miami. Weather was 900 foot ceiling with 3 miles vis. Two 747s were holding short of Runway 12/30 on Taxiway T and on Runway 09 (both were pointed east waiting to cross Runway 30; preparing to depart on Runway 27). As we passed 800 ft on the glideslope for Runway 30 with the runway in sight (100 ft below the ceiling) and the autopilot off; the glideslope began to dive for the ground. The glideslope interference was occurring from the two jumbo aircraft holding short of Runway 30. We reported the interference to Tower immediately. The jet behind us shortly reported the same anomaly after we landed. Had an autopilot been engaged; the aircraft would have commenced a dangerous dive beneath that PAPI visual path or ILS glideslope toward the ground. Glideslope interference from two large aircraft holding abeam the landing runway. Do not allow jumbo aircraft to hold short of Runway 30 when instrument condition are less than VFR conditions.

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	1611481
Time
Date	201901
Local Time Of Day	0601-1200
Place
Locale Reference	MIA.Airport
State Reference	FL
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	ATC Issue All Types Deviation - Procedural Published Material / Policy

B737 first officer reported a glideslope anomaly on the ILS to runway 30 at mia apparently caused by B747 aircraft holding on the taxiway in the vicinity of the end of the runway.