Smolensk Tu-154: Callouts, Decision Height, and Radar Line-of-Sight
Scope. The following is limited to the radar callouts as transmitted, the geometry of the 100 m decision height relative to runway 26, the terrain profile on final, and the documented effect of that terrain and intervening trees on radar visibility. No investigator conclusions are restated.
1. Radar callouts as given
The landing-zone controller issued a sequence of distance-and-path reports, each in the form “[distance] on course, on glideslope”:
- ~8 km — on course, on glideslope
- ~6 km — on course, on glideslope
- ~4 km — on course, on glideslope
- ~3 km — on course, on glideslope
- ~2 km — on course, on glideslope
No callout in that sequence indicated a course or glideslope deviation or directed a go-around. Under the protocol of a radar-assisted approach, “on course, on glideslope” means the aircraft is inside the allowable tolerance. The first non-affirmative instruction (“Horizon 101”) occurred only after the aircraft was already well below 100 m.
2. Position at 100 m decision height
On the published ~2°40'–3° glideslope, 100 m above runway elevation places an aircraft approximately 1.9–2.3 km from the threshold of runway 26. Both the recorded flight path and the controller’s “2 km” call place the aircraft near that distance when it reached 100 m. At that range, and with reported visibility of 200–400 m, neither the runway threshold nor the mobile APM projectors (sited ~200 m from the threshold) were within visual range.
3. Terrain relative to runway elevation
The approach crosses a depression before the threshold. Terrain elevation in that area is lower than the runway. The first tree strike occurred ~1,100 m from the threshold while the aircraft was already ~15 m below runway elevation. An aircraft reporting 100 m radio altitude over the depression is therefore lower relative to the runway surface than the same reading would indicate over flat ground.
4. Radar line-of-sight at low altitude
Trees along the final approach exceeded allowable obstacle-limitation heights in multiple segments between roughly 400 m and 900 m from the threshold (by 5–8 m in several places). Combined with the terrain depression, these trees reduced both optical and radar visibility of aircraft on final. Once an aircraft descended into the depression and below the height of the intervening trees, continuous radar contact was no longer assured. Contemporary technical assessments placed the practical end of reliable radar tracking in the last 1–1.5 km.
5. Callouts versus radar coverage
The final affirmative callout (“2 km on course, on glideslope”) was given as the aircraft entered the segment where terrain drop and intervening trees reduced or eliminated reliable radar contact. According to the content of the callouts, the aircraft was still being reported as on the correct path at that point. The first corrective instruction arrived only after the aircraft was well below 100 m and inside the zone where radar line-of-sight was compromised.
6. Recordings
The tower communications were transcribed, and those transcripts were published by both the Interstate Aviation Committee and the Polish side. The original physical tapes, however, were not released by Russia. Polish investigators worked from digital copies made under restricted field conditions in Russia. Requests for laboratory-quality copies of the original tapes were not fulfilled. That limitation applies to the entire tower record underlying the published transcripts.
Summary of callout content, decision-height geometry, terrain profile, and radar line-of-sight constraints only. No additional interpretation is added.
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