diff --git a/src/app/components/jet-trajectory-chart/jet-trajectory-chart.component.ts b/src/app/components/jet-trajectory-chart/jet-trajectory-chart.component.ts
index 3553da411de0db17b9ba9140b202cb75635dc393..d04c5a3d2200e258c708de2cc0ec4f47f8df1aba 100644
--- a/src/app/components/jet-trajectory-chart/jet-trajectory-chart.component.ts
+++ b/src/app/components/jet-trajectory-chart/jet-trajectory-chart.component.ts
@@ -225,7 +225,7 @@ export class JetTrajectoryChartComponent extends ResultsComponentDirective {
             tension: 0,
             spanGaps: true,
             showLine: "true",
-            fill: true,
+            fill: (nub.prms.ZF.singleValue > 0), // if ZF < 0 chartjs "fills" upwards until 0
             borderColor: "#753F00",
             backgroundColor: "#753F00",
             pointRadius: 0