A318/B738, Nantes France, 2010
A318/B738, Nantes France, 2010
On 25 May 2010 an Air France Airbus A318 making an automatic landing off an ILS Cat 2 approach at Nantes experienced interference with the ILS LOC signal caused by a Boeing 737-800 which was departing from the same runway but early disconnection of the AP removed any risk of un-correctable directional control problems during the landing roll. Both aircraft were operating in accordance with their ATC clearances. Investigation attributed the conflict to the decision of TWR not to instruct the A318 to go around and because of diminished situational awareness.
On 25 May 2010, the crew of an Airbus A318 (F-GUGC) being operated by Air France on a scheduled passenger flight from Lyon to Nantes making an automatic landing on runway 03 at destination off an Instrument Landing System (ILS) approach made in day Instrument Meteorological Conditions (IMC) but with normal on-ground visibility was obliged to disconnect the AP prematurely after observing a directional deviation of the aircraft during the landing roll. Landing clearance had not been given until the aircraft was below DA because of a Boeing 737-800 (F-GZHD) being operated by Transavia France on a passenger flight from Nantes to Djerba, Tunisia taking off from the same runway.
An Investigation was carried out by the French Bureau d'Enquêtes et d'Analyses (BEA). The annotated aerial view of the runway below, prepared by the BEA during the Investigation, includes various key timings and positions in respect of the relative progress of the two aircraft involved in the incident.
It was established that LVP had been implemented at Nantes because of the prevailing cloud base (BKN at 200 feet) and that the arriving A318 was aware of this and as a result, preparations for an ILS CAT 2 approach were made which required the aircraft commander to become PF. ATC were not informed of this intention - but this is not an ATC requirement at Nantes. Subsequently, the Nantes APP controller cleared them to intercept the runway 03 ILS and “reduce speed at their convenience”.
As the aircraft became established on the ILS at a range of 6 nm with a speed of 180 KIAS, the crew advised APP that they were showing a significant tailwind. Meanwhile, the TWR controller was clearing the departing 737, which was approaching the full length runway holding point, to line up and take off. Almost immediately, TWR received the first call from the A318 and asked it to reduce to “minimum approach speed”. Shortly after this, having observed that the 737 had not yet lined up, the TWR controller was told by the crew that the lit stop bar at the holding point had not been extinguished. After it had been switched off, the 737 entered the runway and was in position on the runway and powering up for the take off when the inbound A318 was 2nm from touchdown. The latter was advised of the departing traffic but the Captain of the A318 subsequently stated to the Investigation that information provided by the controller “was not assimilated in a way which would have increased his vigilance or initiated a particular reaction” and the First Officer had “assumed that (the departing aircraft) was more advanced in its take-off sequence”. The lack of any explicit “reaction” in the response of the A318 crew to information about the departing aircraft “led the controller to believe that (the inbound aircraft) was making a CAT 1 ILS approach, reinforcing his decision not to order a go around”.
On becoming visual, both crew “were surprised to see (the 737) on the runway”. The Captain “thought that if the approach were interrupted there would be the risk of a collision with (the other aircraft) in its initial climb, in the absence of any external visual references” and “he therefore decided to continue with the approach”. Nine seconds after the 737 became airborne, the TWR controller issued a landing clearance to the A318, which by then was at 90 feet aal had already descended through the applicable DH of 118 feet.
Interference to the ILS LOC signals detected by the A318 began 4 seconds before touchdown when the departing 737 was passing 58 feet agl, with some 720 metres still to run before it passed over the ILS LOC antenna just beyond the end of the paved surface and continued for a further 8 seconds. The 737 passed over the LOC antenna at 307 feet agl. The effects of this signal interference were not detected by the A318 crew until just after touchdown some 260 metres beyond the runway threshold when the AP had commanded a rudder deflection of 6° left. In response, the PF had disconnected the AP at 90 KIAS instead of the Company SOP of disconnection only after touchdown and “once it has been verified that the landing track has been maintained”. The signal interference ceased when the A318 was at taxi speed and the 737 was 720 metres beyond the LOC antenna.
The Investigation noted that EU-OPS requires that CAT 2 approaches require LVP, which were still in force and that Air France procedures require that any CAT 2 approach must be followed by an automatic landing.
In respect of ATS at Nantes, it was found that:
- Nantes ATS procedures state that “Clearance to land is not normally given to an aircraft on approach until the ILS hot spots (such as the one at Holding Point ‘A’) are clear; the said aircraft must also be more than 2 NM away from the runway threshold” but that “clearance may be delayed until the aircraft in approach is 1 NM from the runway threshold, provided that the hot spot is clear, the crew has been given advance warning that clearance would be late and the position of the aircraft in approach may be monitored via radar”.
- In respect of separation between aircraft landing and aircraft taking off from the same runway, Nantes ATS procedures state that “it is essential that aircraft taking off have passed over the emitting antenna of the ILS localizer before any landing aircraft reach the point in their approach where the interference caused by the over-flight may have a critical effect” and that the “objective is for the aircraft taking off to have passed over the localiser antenna before the aircraft on approach reaches 2nm from the runway threshold”. They further state that “to achieve this result, the departing aircraft must start taxiing for take-off before the aircraft on approach reaches 6 nm from the runway threshold”.
- It became apparent during the Investigation that controllers at Nantes had various degrees of understanding about how the lit stop bar at the full length holding point ‘A’ where the 737 entered the runway for take off could be controlled and the effect of the sensing circuits ahead of and after it. Some “were in the habit of waiting for the aircraft to be detected by the first circuit in order to avoid setting off the intrusion alarm or reactivating the lit stop bar at an inappropriate time” whilst others “believed that the system logic required an aircraft to be detected before the lit stop bar can be turned off”. The TWR controller in position at the time of the incident stated that he had not switched off the stop bar when clearing the 737 to line up because he had intended to wait for the ‘prompt’ to do so triggered by the taxiing aircraft as it approached.
- Nantes local ATS procedures state that CAT 2 approaches are not permitted if an aircraft with a height exceeding 10 metres is on the parallel taxiway between Taxiway ’B’ and Holding Point ‘A’. However, “there is no standardised control method associated with this instruction” and since crews are not required to advise when making a CAT 2 approach, controllers will not necessarily be aware when this restriction applies.
The formally-recorded Conclusion of the Investigation was that “the incident occurred as a result of the tower controller’s decision not to instruct (the approaching aircraft) to (go around) and because (the departing aircraft) took off as soon as its position between Bravo and Alpha was noticed and while LVP separation standards were no longer verified”.
The Final Report of the Investigation was issued in a French language version only in September 2011 and is also available here on SKYbrary in an [unofficial English language translation]. No Safety Recommendations were made and no Safety Action reported.