FAQ #6 Update: Landing by night – just as by day – the Jacobson Flare
FAQ #6 Update: Landing by night – just as by day – the Jacobson Flare
A recent question became a timely reminder that an expanded explanation on how to adapt the Jacobson Flare principles to night landings was overdue. So, for current exponents of the JF, here is a suggestion that can tune your night landings into the same, exacting standards that you are now achieving, by day. It updates the information, previously found in FAQ #6, at https://www.jacobsonflare.com/our-most-frequently-asked-landing-questions/
Disclaimer
This is a technical dissertation, intend primarily for more-experienced pilots and to provide an interim supplement to the Jacobson Flare App. Less-experienced pilots are advised to treat the information contained herein, as information, only. Please, do NOT attempt to apply the information, contained herein, if you are a new or yet-to-be user of the Jacobson Flare.
It’s generally NOT a good idea to do anything in an airplane, for the very first time! By this we mean, do it with someone, preferably a flight instructor, who has done it before. Your safety is paramount. So, become proficient at using the Jacobson Flare by day, before attempting to apply it at night.
This information is directed more specifically to pilots of 4-6 place single- and twin-engine-airplanes, below 12,500lb/5,700Kg MTOW, operating onto runways without glideslope guidance.
Any study or application of this content should not be rushed, if full comprehension is to be achieved.
Pilots of larger airplanes should be able to relate the principles to their current airplane, although the aircraft landing lights generally illuminate the runway fixed distance markings well, which helps to identify both the correct visual aim point 1 and the pre-calculated flare cut-off point for the airplane type. Alternatively, please feel welcome to contact info@jacobsonflare.com for further information.
Background
Early in the research and development of the Jacobson Flare, around 1985-87, I was a civilian flight instructor at the RAAF Point Cook Flying Club, in addition to my full-time career as an airline transport pilot – at that time, a DC-9-30 line training captain with Trans-Australia Airlines (TAA)/Australian Airlines.
I am not ex RAAF, myself, but was in the ‘right place/right time’, from 1983-89), in a more-or-less voluntary capacity.
The following technique was flight-tested and proven, in C150, PA-28 and PA-38 aircraft, on Runway 17 at RAAF Base Williams, at Point Cook -YMPC – a classic ‘black-hole’ runway, at night, located SW of Melbourne.
When headed away from the lights of Melbourne city, the immense Port Phillip Bay is the black backdrop and, depending on the prevailing conditions. it can be difficult to discern the horizon. The lights of the Melbourne SE shoreline suburbs are not much help, either, when late on final approach for a landing on 17.
There is no T-VASIS, PAPI or ILS glideslope to ‘hang your hat on‘, so it was a ‘Mk 1 eyeball’ approach. However, this solution proved to work perfectly at YMPC and can be adapted easily to the night situation, at other locations.
Note: If visual glideslope guidance, such as a PAPI system, is available at a particular airfield, then the PAPI aim point comparison calculator (standard in the Jacobson Flare App), together with the published runway edge lighting spacing and the following information, can be applied to ascertain and then optimise the actual PAPI aim point 1 and flare cut-off point for the subject aircraft, in night operations.
Let’s take a look at the following standard 5 JF considerations, to re-examine what we use by day and what we can adapt for night landings.
Note: The ft/m conversions have been rounded, for convenience. This makes no practical difference to the landing outcome.
The 5 Jacobson Flare Considerations – Applied to Night Operations
- Where to aim?
The JF-suggested visual aim point, for 4-6 place single- and twin-engine-airplanes below 5700Kg MTOW, located at 300ft/90m from the threshold is still ‘King’, to assure approximately 10ft threshold clearance of the main landing gear (MLG). By day it’s the ’top’ of the first centre line mark, past the runway numbers. So it is, normally, by night. Now, the runway edge lighting is a great reference, as you can use the normal (i.e., 90º) axes across the parallel pairs of edge lights, to determine suitable longitudinal references for both the aim point 1 and the flare point.
The standard runway edge lighting spacing is 60m , but a detailed check of this information confirms RAAF Point Cook -YMPC has a non-standard spacing of 85.6m (approx 90m). Like many things in aviation, edge lighting spacing is not as standard as it might be: For example, Australia’s busiest GA training aerodromes: Adelaide Parafield YPPF 03L/21R, Brisbane Archerfield YBAF 10L/28R, Melbourne Moorabbin YMMB 13L/31R and 17L/35R and Sydney Bankstown YSBK 11C/29C, have their runway edge lighting spaced at approx 90m intervals, yet Perth Jandakot YPJT 06L/25R and 12/30 has the runway edge lighting spaced at the standard 60m intervals.
Fortunately, these variations are covered by the 1:20 tolerance of the unique longitudinal flare point principle of the Jacobson Flare. This point is explained, below, in 3. When to flare?
Note: In addition, YSBK 11C/29C and YPJT 24R each have 3º PAPIs, with 25ft MEHTs.* (*Minimum Eye Height at Threshold)
By night, the runway threshold is marked by the standard runway threshold green lights.
- At 200ft/60m standard spacing, the 300ft/90m aim point 1 would lie mid-way between the axes of the first and second pairs of edge lights; the flare cut-off point is 100ft/30m back from aim point 1, at 200ft/60m, exactly on the axis of the first row. See the 60m spacing illustration in Fig 1, below:
Fig 1
- At 300ft/90m spacing, aim point 1 would fall exactly on the axis across the first pair of edge lights, at 300ft/90m. However, the flare cut-off point would lie 100ft/30m back from there, at 200ft/60m, unserved by any usable or consistent visual cue at night, except the aircraft landing lights. See the 90m spacing illustration in Fig 2, below:
Fig 2
Having different aim- and flare-point indicator cues at night, for the same actual aim and flare point locations is less than ideal; and you may or may not have the luxury of being able to check the light spacing before you land somewhere. In any case, the quality of this data may not be all that accurate.
So, to keep things simple, consistent and conservative, let’s establish a single, consistent assumption for all aerodromes that you are likely to use at night:
We have established above that, at 200ft/60m standard spacing, the 300ft/90m aim point 1 would lie mid-way between the axes of the first and second pairs of edge lights; the flare cut-off point is 100ft/30m back from aim point 1, at 200ft/60m, exactly on the axis of the first row.
Now, if the spacing was actually 300ft/90m – BUT, we aimed at the same NIGHT aim point 1, mid-way between the axes of the first and second pairs of edge lights, then the ACTUAL aim point 1 location would be located at 450ft/135m, somewhat deeper.
Given that the certified landing distance is factored (increased) by 67%, this is not a practical issue, as long as the approach is flown accurately, within +5/-0kts. See the 90m spacing illustration in Fig 3, below:
Fig 3
- How to aim?
No change is needed. Fly the same aim point 1/glare shield relationship as by day, controlled with the elevators and the airspeed controlled with power/thrust – to achieve the essential stable approach path.
Aim point 1, as discussed above, is the mid-point of the imagined axis, longitudinally mid-way between the axes of the first and second pairs of edge lights; in other words, the centre of the black space between the first 4 edge lights.
Now, many pilots find that, at night, things seem to be happening ‘faster than by day’, as the airplane approaches the runway, on short final. This may be due to our eyes ‘zooming-in‘, like a camera lens, on the pre-dominant object in the pilot’s view: the runway shape, outlined by the threshold and edge lighting. The rest of the airfield is often very dark.
It has been found very useful to imagine the airfield as it appears by day, or imagine wearing night-vision goggles, so the visual field more resembles the daylight view: the pilot’s eyes don’t ‘zoom-in‘ and the approach groundspeed appears more ‘normal‘.
- When to flare?
This where the 1:20 advantage of a longitudinal flare point assists, greatly. We already know that the flare cut-off point is 100ft/30m back from aim point 1 – for 4-6 place single- and twin-engine-airplanes, below 5700Kg MTOW.
For 200ft/60m spacing, aim point 1, mid-way between the axes of the first and second pairs of edge lights, is perfectly located at 300ft/90m, so the flare point will be located on the axis through the first pair, at 200ft/60m, exactly as by day.
As stated above, if the spacing was 300ft/90m – and we aimed at the same NIGHT aim point 1 cue, mid-way between the axes of the first and second pairs of edge lights then the ACTUAL aim point 1 location would be located at 450ft/135m, somewhat deeper. The correct flare cut-off point for that aim point location would lie 100ft/30m back from there, at 350ft/105m.
However, to be consistent with the 200ft/60m case, we might wish to use the same flare point indicator, namely the axis of the first pair of edge lighting, at 300ft/90m. This would create an actual flare cut-off distance of 150ft/45m: an error of 50ft/15m.
Yes, it’s a little earlier – and correspondingly higher, BUT:
The longitudinal error is 50ft/15m: Applying the 1:20 advantage, (dividing by 20) indicates a diminished vertical error of just 2.5ft/0.75m. This is well within the vertical tolerance of any landing, flared using the conventional ‘educated guess’ of height.
Speaking of flare point tolerance, it has been found useful to regard the flare point much like a CG, lying within an acceptable range between a forward and an aft limit. This an example of that comparison. Now, at a normal 3-4º approach path angle and flaring over the usual 4-seconds to a new aim point 2, probably at least 2000ft/600m away, or even further, it makes little difference whether you flare at the aft limit, the forward limit, or anywhere in-between: it is relatively insignificant.
Review Figs 1 and 3, above: The edge lighting spacing is different, but we can use the same visual cues for both the aim point 1 and the flare point, for runway edge lighting spacing of 60-90m spacing and the 4-second flare will smooth out the variations in actual flare cut-off distance, between the aim point 1 and the flare point, due to the 1:20 tolerance of using a longitudinal flare cue.
Finally, use EVERY cue at your disposal, including your experienced assessment of vertical flare height, too. Triangles still have three sides! We might as well use all of them.
Airline fleets and other advanced types offer the added advantage of computer-generated call-outs of ‘100..50.. 40.. 30.. 20.. 10‘ ft radio altitude (‘radalt‘), from the ground proximity warning systems (GPWS). However, these are still subject to certain limitations, such as radio interference and the mathematical fact that, on the standard 3º flight path angle, every +/- 1ft vertical error compounds as a longitudinal error of +/- 20ft respectively, along the runway.
- How much to flare?
Again as by day, transition to aim point 2, at the end of the runway lights. For a runway of uniform slope – not necessarily level – this is the same as used by day: the upwind threshold.
For undulating runways:
Where the landing zone is located on a downhill slope, aim point 2 is relocated to the ‘bottom end‘ of that downhill slope, before the runway becomes more level; geometrically, the flare cue will occur later/lower than the level-runway case. (* See this app Pp 93-95)
Where the landing zone is located on an uphill slope, aim point 2 is relocated to the ‘top end‘, or ‘brow‘ of that uphill slope, before the runway becomes more level; geometrically, the flare cue will occur earlier/higher than the level runway case. (* See this app Pp 93-95)
This technique will assure a more accurate convergence with the landing zone surface in each case.
- How fast to flare?
The usual Jacobson Flare 4-second technique, or maybe stop the flare at 3-3.5 seconds, if the runway has a lot of water on it, to reduce the risk of aquaplaning.
(In a jet transport airplane, aiming at aim point 2, after completing the full, 4-second flare, can result in too-smooth a landing! The main wheels don’t penetrate the water layer and make proper ground contact, so apart from the risk of aquaplaning, the main wheels don’t spin up to about 700rpm and, in some airplane types, the pre-armed auto brakes and auto-spoilers don’t actuate – they actually get ‘confused‘.)
So, there you go. It’s a bit to digest: Try drawing it out on some paper, to scale for your airplane; think it through; sit in a chair and visualise the whole thing. And try it, first time, with someone else, preferably a flight instructor, with you, or better still, have a play in a simulator. It may be very beneficial, to prove it to yourself, first.
Use all available cues, including the landing light-illumination of the centreline and fixed distance runway markings and your accumulated experience, (together with the GPWS ‘radalt’ callouts in larger aircraft), in assessing your height above the runway.
Of the three components to any landing:
1. The initial pilot’s eye path to aim point 1;
2. The commencement point of the flare; and
3. The flare, itself, through to the second aim point, usually at the far, upwind threshold:
The first is the most important; second most is the third and the least important is the flare initiation point, so long as it is within that ‘range of acceptable flare points/heights‘ for the airplane type, as discussed above.
Finally, to reiterate, the one aim point 1 – at 1.5 rows of edge lights – and the one flare point – at the first row of edge lights – may be applied for runway edge lighting spacing of 60-90m spacing and the 4-second flare will smooth out the differences. See the generic spacing illustration for 60-90m edge lighting spacing in Fig 4, below:
Fig 4
Wishing you many safe landings
Captain David M Jacobson FRAeS MAP
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