What is an ILS PRM approach and how is it flown?

An ILS PRM approach is an Instrument Landing System approach flown simultaneously with traffic approaching a closely spaced parallel runway, protected by Precision Runway Monitor radar and dedicated controllers. Pilots fly the ILS normally, monitor a second radio frequency and execute any controller-issued breakout immediately; crews must meet the published training and equipment requirements.

In our Aviation & Real-World Flying coverage, PRM refers to the surveillance and ATC operation, not a stronger or more accurate ILS signal. The term is used chiefly in United States procedures; equivalent close-parallel operations elsewhere may have different names, qualifications and communication rules.

What does PRM add to a normal ILS approach?

PRM adds protection for simultaneous approaches to runways too closely spaced for ordinary independent parallel operations. A dedicated monitor controller uses high-update surveillance to detect an aircraft drifting towards the adjacent final approach course.

A protected no-transgression zone, normally 2,000 feet wide in US PRM operations, lies between the final approach courses. Predictive alerts give the monitor controller time to issue a breakout before a deviation develops into a collision risk.

PRM does not make the ILS a CAT II or CAT III approach, and it does not automatically reduce the decision altitude. The minima printed on the specific ILS PRM chart remain controlling.

How do you fly an ILS PRM approach?

Fly the localiser and glideslope like a conventional ILS, but complete the additional PRM briefing, monitor both assigned frequencies and remain ready for an immediate breakout.

1. Confirm eligibility before accepting. For a US PRM clearance, the pilot must have completed the prescribed PRM training. Check operator authorisation where applicable and all charted equipment requirements, typically including two operable VHF communication radios. If any requirement cannot be met, tell ATC UNABLE PRM early.
2. Brief the complete PRM procedure. Review the ILS PRM chart and its associated Attention All Users Page. Cover the localiser frequency and course, glideslope intercept altitude, minima, published missed approach, parallel runway, monitor frequency and breakout procedure. Our guidance on building a complete ILS approach briefing covers the underlying items that still apply.
3. Set up and verify the correct ILS. Tune and identify the localiser, set or verify the inbound course, select the proper navigation source and cross-check the runway designation. Closely spaced runways make selecting the adjacent runway's ILS a particularly serious error.
4. Configure both communication radios. When instructed, use the primary radio for tower communications and select the published PRM monitor frequency on the second radio with its audio enabled. Continue transmitting on the assigned tower frequency unless told otherwise; the second radio lets the monitor controller reach the crew directly.
5. Capture and track normally. Intercept the localiser without overshooting, capture the glideslope from below and confirm the expected flight-mode annunciations. The approach may be hand-flown or coupled when permitted, but the crew must still monitor lateral tracking closely.
6. Maintain the cleared course. Do not sidestep towards the other runway or manoeuvre merely because parallel traffic looks close. At the decision altitude or height, land if the required visual references and stability criteria are satisfied; otherwise fly the published missed approach unless ATC has issued different instructions.

What happens during a PRM breakout?

A PRM breakout is an immediate ATC escape manoeuvre issued when an aircraft threatens the protected space between the parallel approaches. It is not the same as a normal go-around or published missed approach.

1. Start the commanded manoeuvre immediately. Follow the stated turn direction, heading and altitude instruction. Do not delay the turn while completing a full readback.
2. Manage automation without sacrificing response time. Follow the aircraft's operating procedure; disconnect the autopilot and hand-fly if that is the quickest reliable way to produce the commanded turn and vertical response.
3. Acknowledge once the response has begun. The pilot monitoring should confirm the instruction and watch airspeed, configuration, altitude and traffic while the flying pilot concentrates on the breakout.
4. Obey any TCAS resolution advisory. A resolution advisory takes precedence over an ATC breakout instruction. A traffic advisory alone does not authorise a self-directed evasive turn.

The breakout instruction replaces the approach clearance. Do not add the published missed-approach turn or altitude unless ATC subsequently directs it; doing so could turn the aircraft back towards the conflict.

Can a pilot refuse an ILS PRM clearance?

Yes. A pilot should decline when the crew lacks PRM training, required equipment is inoperative, both frequencies cannot be monitored or another operational limitation prevents safe compliance. State UNABLE PRM; ATC may provide another approach or impose a delay.

Common ILS PRM mistakes

Most PRM errors come from treating it as either an ordinary ILS or an automatic reason to avoid nearby traffic.

• Using the wrong chart or localiser: verify the runway, chart title, frequency, identifier and inbound course independently.
• Leaving the monitor radio muted: select its audio and set a usable volume before final approach.
• Reading back before turning: begin an urgent breakout first, then acknowledge it.
• Flying the published missed approach during a breakout: follow the breakout heading and altitude instead.
• Reacting to expected parallel traffic: remain on the localiser unless ATC issues a breakout or TCAS commands an RA.
• Relying entirely on the autopilot: monitor the localiser trend and be ready to take manual control without hesitation.

Can an ILS PRM approach be practised in a simulator?

Only part of the operation can be reproduced without dedicated controllers and simultaneous parallel traffic. Most built-in simulator ATC systems do not model the separate monitor frequency, no-transgression-zone prediction or authentic breakout instructions.

You can still practise the aircraft handling: use the appropriate chart, configure both radios, fly the normal localiser and glideslope sequence, then have an instructor or controller issue an unexpected breakout heading and altitude. Our simulator ILS procedure covers capture, mode monitoring, configuration and minimums. Selecting an ILS PRM frequency by itself does not create a genuine PRM operation.