Cambridge through the murk

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I had a good excuse to fly this week – a business trip to Cambridge. The choice between over 7 hours by car or 42 minutes each way by plane isn’t a difficult one to make, even after adding an hour to get to Gloucester airport. The TB20 was free as it often is during the week, so I booked it up early.


A warm front had been causing high levels of pollution for days, with haze and poor visibility. I initially cancelled the flight but then reconsidered the day before, treating this very much as an IFR trip.

I submitted the PPR form to Cambridge by email the day before. No reply, so phoned them to check all OK and ask if I could get a radar vectored ILS on request. Cambridge don’t always have their radar service available (it’s not always manned), so it was nice to know I could expect it.

Called Gloucester ATC and booked out IFR with a cruising altitude of 5000 feet – should be high enough to be above the clag but below the airways at FL55. The calm winds meant either runway could have been in use for departure, but the ATIS advised 09 which meant a long taxi to the hold. On calling up the tower for taxi, I was advised the runway had changed to 27 which made things simpler. With visibility in the haze down to about 4000 metres and overcast at 1200 feet, there was very little other activity at the airport.

Climbing into the soup

After a standard departure, I climbed into the soup and turned east. I was cleared direct to Cambridge, own navigation climbing to 5000 feet. I had planned to route slightly to the north of direct track, via Towcester, which would take me north of Hinton in the Hedges, often an active parachuting base.

The autopilot was set to follow the heading bug while I ran through regular checks – ensuring fuel pump off, pitot heat on, altimeters set, icing checks etc. – and frequently adding manifold pressure to maintain power. I popped out of the cloud at about 3500 feet, but continued with a cruise climb up to target altitude. Daventry VOR was dialled in as a useful navaid, and I played with swapping between the VLOC and GPS modes on the GPS. Brize Radar gave me a traffic service at my request, but there was nothing to report and it was very quiet. Perhaps because of my higher level, Brize continued providing a service for longer than I expected – well to the east of Banbury where I normally expect to be transferred.

VMC on top
VMC on top

Unexpected change of runway

Cambridge ATIS reported Information Papa, Runway 23 in use, wind relatively calm. I omitted to mention the ATIS code letter on first contact with Cambridge Radar, so they advised me that Information Romeo was valid, passing QNH and runway in use. It had changed to 05, which caught me unawares. I was asked what approach I’d like so without thinking proposed the RNAV for 05. I was instructed to navigate to BEBOX, the initial approach fix. I later re-listened to the ATIS which was still giving Papa.

Clearly, having not expected this approach, I didn’t have the plate ready or the approach loaded. While I tried to sort this out, Radar queried as to why I hadn’t changed direction. I asked for an initial Radar heading and was not only given this but the offer of radar vectors for the RNAV approach. I’d not come across this before so took full advantage – it’s the same as a radar vectored ILS. I was given a couple of headings to steer and cleared to progressively lower altitude. I had by then activated the approach on the Garmin GTN650 but kept the autopilot on heading mode rather than NAV or APProach. I descended into the murk. Visibility was reported as 3800 metres.

As I approached the final approach track, I was told to intercept and report base turn complete.

RNAV without advisory glideslope

This RNAV approach is a non-precision approach. Not only does it not have a calibrated glideslope, but this one didn’t show an advisory glideslope. It’s much more akin to the older NDB/DME style of approach. A continuous descent profile should be set and checked at set distances before touchdown. I incorrectly reported “localiser established” which Radar pointed out (should have said “Base Turn Complete”). My initial descent rate was a little too fast, then I overcompensated and remained a little too high. The runway came into view dead ahead when at about 1000 feet, somewhat high but allowing a gentle glide descent down for a good landing.

Park and Ride

Having been to Cambridge before, I was able to park on the grass and put the cover on. Short walk through to the Aero Club where I got a discounted rate by having joined their (free) mailing list.

There’s a Park and Ride bus stop outside which whisks you straight into the city for about £2. I’m sure it’s just as quick as a taxi.

Slightly delayed departure

My return the next day was at my own pace. The haze again reduced visibility to 3800 metres. After booking out at the desk, I walked out wearing the mandatory yellow jacket. Runway 23 in use, so taxied to Alpha for checks. On reporting ready, there was a delay of a couple of minutes while a jet landed and a training aircraft made a practice approach. My departure clearance was to climb straight ahead to 5000 feet with a discrete squawk.

I was held lined up on the runway for a few minutes – Radar wasn’t willing to release me while there was another aircraft bimbling about on the departure path given the low visibility. While I don’t really like hanging around on the runway, this seemed the better option. While I waited I requested a revised clearance to turn right onto track at 3000 feet.

Sunny side up

After departure I was quickly into the soup at about 1000 feet and concentrated on maintaining the climb. You really have to trust your instruments in these conditions, despite what your body tells you to. Radar cleared me to resume own navigation after passing 2000 feet and I turned West while continuing the climb. Gradually crept above the murk at around 4000 feet to find glorious sunshine and a fluffy carpet of cotton wool clouds all around.

5000 feet
5000 feet

The route back was very much retracing my outbound path. I only asked Brize for a Basic service at first, since I had good visibility all around. Surprisingly, Hinton in the Hedges was said to be active with parachuting up to FL130. Once west of Banbury, Brize asked me what type of approach I would like on my return to Gloucester. I requested a straight in for the RNAV for 27 joining at NIRMO which they co-ordinated, telling me that Gloucester would accept me at 4000 feet. I activated the approach and let the autopilot fly direct towards NIRMO, slightly to the left of direct track to Gloucester.

VMC on top - south
VMC on top – south
VMC on top - North
VMC on top – North

With the cloud tops at 4500, I wasn’t too keen to descend any earlier than I needed to. The ATIS reported cloud base of 3000 feet and runway 22 in use. The RNAV for 27 has a platform height of 2500.

Choice to delay or drop into the cloud

My dilemma was that Brize could give me a radar service which Gloucester couldn’t. I wanted to remain VMC on top as long as I could, then remain with Brize for a traffic service during the IMC descent. But I also wanted to descend at a controlled rate and be at 4000 feet before talking to Gloucester. I later clarified that Gloucester don’t have a specific handover point from Brize when traffic is co-ordinated in this way.

I requested and was given a Traffic service prior to descending through the cloud layer, resulting in rapid fire advice of three “targets”, none of which seemed to be an immediate threat. At 4000 feet, I requested a further descent but Brize denied that and reminded me that Gloucester had authorised acceptance at that altitude. I then transferred to Gloucester who provided a Procedural Service, clearing me for the approach. I could descend down to platform height, clearing most of the cloud at 2800 feet. Having remained high later to reduce the time in IMC, a descent rate of 1000 fpm was needed to get me down to 2500 feet by NIRMO with the autopilot was engaged in approach mode. It caught the glideslope at the Final Approach Fix and flew down nicely with the runway coming clearly into sight. Onto manual and full flaps at about 500 feet for a good final approach and touch down on 27. Immediately after, another aircraft was cleared to land on 22 and I was directed to taxi around the edge of the airfield back to parking. I really like the way Gloucester can intersperse traffic on two runways efficiently in this way.


Many would see this trip as a pretty straight forward short flight, climbing to VMC top and returning using standard instrument approaches. I haven’t done that much of this solo before (for real), so it is still new to me and far from perfect. Making best use of the available radar and ATC services, not descending earlier than necessary and erring on the cautious side all seemed to be good strategies.

I was still caught out by the unexpected change of runway at Cambridge and could do with a bit more practice of RNAV approaches without advisory glideslopes. Perhaps I should anticipate a runway change and already have a Plan B in mind if and when that happens.

Outbound Gloucester to Cambridge
Inbound Cambridge to Gloucester

Total PIC this trip: 2:00 (of which 1:20 airborne)

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