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IFR pilots are always talking about the Minimums - referring to the point after which a go-around must be done if the runway is not in sight. ILS Category I are the approach with the lowest possible minimum that a single pilot in a single engine plane can fly, the standard minimums then being 200 feet ceiling, and 550 meters visibility. So what ?

This definition is not so easy to imagine for non IFR pilots, so let me give some hints. Let’s assume a high performance single, like a Saratoga. The final approach speed is 90 knots, which on a standard 3° glide slope corresponds to a descent rate of 472 feet per minute… To say that differently, the aircraft is only 25 seconds away from hitting the ground - a bit more from a normal landing, because of the flare.

The distance between the place where the plane reaches the descision height (200 feet) and the touch down-zone is 0.625 nautical miles. If the runway (or the lighting system) is in sight at this point, the pilot can continue to land visually. Depending of the aircraft type and runway length, this could include the deployment of the final stage of flaps. I also like to do the final check again when deciding to land - the good old red (mixture) blue (prop) green (landing gear).

If you still can not imagine what the runway looks like from the minimum, look at the pictures below. They have been taken from a DA40, approaching and at the minimum on the ILS approach to runway 23 in Geneva. The lighting system is already out of sight, even if the plane is not actually overflying it yet. This is a very standard 200 feet minima, on a day with perfect visibility.

Geneva, shortly before… and at the minimum !

Some approaches have higher than standard minimas. This can be cause by obstructions in the approach path, or in the go-around trajectory. The two pictures below show the situation before and at the minimum in Farnborough ILS 24 - note the displaced threshold..

Farnborough, shortly before… and t the minimum !

If these minimums seems high to you, remember that they are determined by the position on the ILS, and the altitude. Yes, the altitude, based on the baro-altimeter. It is cross-checked at various moments during the approach, but a mistake is always possible. To speak in millibars (remember, 27 feet per millibar), the minimum is only 7 millibars away from the ground.

The training syllabus is very clear on that point: one shall not fly below the minimum. On IFR proficiency check flight, the allowed margin when reaching the decision altitude is +50 / -0 feet. Go below the minimum, and the check is failed.

Any pilot tempted to fly below the minimum visual contact to the ground should remember that doing so is one of the major cause of pilots and passengers death - together with flying VFR in IMC. Fly safely.

This is the second post in a series about preparing an IFR flight, which I will hopefully do this summer, when visiting friends in England. It will be a Bornemouth - Guernsey leg, and today I’ll give more details about the approach.

In many respects, the ILS approaches to Guernsey are typical, school-like ones. No exotic or special procedures, but many details that must be looked at. For each approach direction (09 - 27), there is an ILS, a VOR-DME and an NDB approach, which follow the same principles.

The approaches start overhead the VOR (or the NDB in case of NDB approach), and start with an outbound leg. Then comes a 45°/180° track reversal procedure to intercept the final approach track.

There is no mandatory holding, but for runway 27, the holding published over the VOR can be used for track reversal, as the turn to the outbound track when coming from the airway would be too steep. I don’t know how likely it is to get vectors to final approach, so I get ready for the full procedure, just in case…

The go-around is always the same as well: fly straight ahead to 2.5, 2.7 or 3.0 miles, depending on runway and approach type, then turn right back to the VOR / NDB and hold. There are also altitude conditions associated with the turn.

That’s for the big picture, now come all the details. At first, both ILS use the same frequency: 108.1. It’s always important to identify beacons using the morse call-sign, to make sure they’re not failed, or undergoing maintenance, but in that case, it’s even more imporant. If for any reason the wrong ILS is in service, this could lead to false indications.

Reading the notes on the approach plates can take time, and it’s better to do that before the flight. One mentions that aircraft unable to receive DME shall advise ATC, and will be given radar ranges at key points of the procedure. I don’t know the reason for that, may be it is because the approach is flown relatively low, at 2′000 feet over the sea, making DME reception less reliable.

The procedure starts at 2′000 feet over the VOR / NDB, and the outbound leg is 7.2 miles long, all at 2′000 feet, so there is no descent planning issue. If starting the approach directly from the airway, at an higher altitude, the standard descente rate of 300 feet / miles means one must not cross the VOR at altitudes above 4′000 feet.

The Decision Altitude (DA) when flying the ILS is at 503 feet AMSL, corresponding to the standard category I 200 feet AGL minimum. The glide slope is also a standard one, descending at 3°.

In case the DME is failed, times are published for the procedure turn, and the missed approach point is then the VOR itself, with obviously a much higher minimum.

Circlings are not forbidden, but there are some prescriptions regarding altitude and tracks. The probability of flying a circling seems very remote, as three different approach types (ILS, VOR, NDB) are available for each runway direction.

After all that preparation, I feel more comfortable with the approach. I will obviously brief the one we’ll fly before executing it, but without a careful pre-study, that would be hard. Any of your tips are also welcome.

If you liked this post, you can read the previous on in the series, about preparing the route from Bournemouth to Guernsey.

This post is the first in a series about airport equipment. If you always wanted to know all what these antennas, lights, signs, markings and other stuff are, you landed in the right place.

These orange antennas located in the extended runway axis are transmitting the “Localizer” signal of the Instrument Landing System (ILS). It is a narrow and precise beam which planes use to line-up with runway axis when landing. They are located at the far end of runway they serve, so the approaching planes don’t have to overfly them.

The beam guiding planes vertically during ILS approach is known as “Glide Path” and is transmitted by three antenna located on a mast beside the runway. On this picture it’s on the left side, but it can be any side of the runway. On a perfect approach, aircrafts cross this mast at the level of the middle antenna.

In front of the mast, you can see white and red lights from the PAPI system. This is a visual vertical guidance system (read more about it here). On ground, the PAPI equipment looks like on this picture.

The simplest tool for radio-navigation is the Non-Directional Beacon (NDB). It’s a simple AM transmitter, sending the same signal in all directions. An on-board direction finder indicates to the pilot where the beacon is relatively to the aircraft. The antenna ground looks like that.

The VHF Omni-Range (VOR) is a more advanced and precise navigation beacon. It sends a direction dependent signal, which the crew can use to determine their position relatively to the beacon. An advanced version of it is the “Doppler VOR”. It is used in sites where terrain can generate reflections. It requires then several antennas organized in a circle.