2011-07 · NASA ASRS report 957332
A319 Flight Crew describes approaching LAS to find strong winds and unforecast weather with no planned alternate. During approach Autothrust does not manage speed as expected; maintaining 10-15 knots fast throughout. Heavy rain commenced shortly after landing. The Autothrust problem reappeared during approach on the next leg.
During a surprise swarm of convective storms in LAS; we found ourselves holding at KADDY intersection on the Tyson 3 arrival. Forecast was for scattered showers but did not require; nor did we get; an alternate. As a strong storm was approaching the west end of LAS; Captain decided to continue to LAS as Dispatch was issuing a diversion to ONT. At the exact moment of the Dispatch message; approach instructed us to make a heading to intercept RWY 25L LOC; and leave the hold. As we approached airport; airspeed would not reduce to final target speed. PF selected Vref; but no change occurred. He disengaged and reengaged the Auto thrust with no change. Aircraft seemed to want to stay at 10-15 kts above ref speed. It never fluctuated; but stayed stable. At 500 AGL callout; speed was not on target; but aircraft was stable. Landing occurred without incident. I must mention ground speed mini never was a factor as wind was steady and low in velocity. Neither Reactive nor Predictive Wind Shear systems activated. We were so busy with WX avoidance and continuing on the approach that an actual cause could not be determined. Our attention was diverted so troubleshooting was not a priority. As we approached LAS; the concern of whether we could continue holding or divert was causing anxiety. We felt we had few options but to land LAS in decent weather; but that was deteriorating rapidly. On our next leg during landing in calm winds and clear skies the same 'target speed' error occurred with me as PF. Upon landing; we entered a discrepancy in the Logbook to have the Auto Thrust system checked.
While flying the ILS to LAS RW 25L we were told to maintain 170 to the FAF. After I managed the speed I noted that the airspeed was not slowing to managed REF speed. It was stable; but at about 15-20 KTS above REF. I selected a REF speed; but this did not seem to have any effect either; as the speed stayed 15 to 20 knots higher than ref. At first I though this might be due to ground speed mini; but a quick check of setting and wind indications eliminated this as a cause. Then I tried resetting Autothrust; but this had no immediate effect. By about 1200' AGL; the speed was still high; but not wavering up and down. I would call it stable but fast. At this time it had decreased to about 10 to 15 fast. The higher speed and staying on the glide path gave us an occasional excursion in rate of descent to between 1000-1200 FPM. As we were descending we could see the weather approaching the airport and dust being blown in advance of the weather. I knew there were a bunch of other flights behind us that had also been caught off guard by the weather and that if I went around; we may not be able to get in before the weather hit; thereby creating a serious fuel emergency for us. By 500' agl; our speed was still 5-8 KTS high; but stable (not jumping around). In light of the situation; which included a 14;000' landing runway; I elected to continue the approach and land. The winds throughout this were not particularly strong; but were from varying directions. I continued the approach and landed uneventfully and turned off at B-6. I think our speed was still about 5-10 KTS above ref when I began to flare at 'retard; retard'. I don't know why the speed would not decrease to ref. The auto thrust had operated normally up to the point where we were on the approach and managed the speed to slow down as previously mentioned. At no time during this whole event did the tower issue any low level wind shear advisories. The on board reactive and predictive systems did not activate either; eliminating wind as the cause of the Autothrust holding a higher speed. After we landed; the weather really deteriorated with heavy rain; strong winds; and lightning. I understand the reluctance of the company to load extra fuel on the planes if the forecast does not indicate weather issues requiring an alternate; but this is the second time I've had a divert situation arise when there was no bad weather forecast and no alternate or alternate fuel. I would suggest that at locations like LAS where there are no good alternates nearby the destination; an alternate should be designated anyway during the summer due to these big storms which can develop so quickly. It would cost a little more; but it would be cheap insurance.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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